Dracovenator

Dracovenator is moving

2009-10-26T23:57:00.000-07:00

For some unknown reason blogger pages just won't load via my university network. For the longest time I've had all sorts of problems with gmail related sites. For instance I've been unable to add attachments to email from my gmail account. Now blogger won't load any of the buttons needed for making a post. So I'm leaving blogger. You can find my new blog at dracovenator.wordpress.com
See! I can't even link to the new site.
Update: OK, this message is now linked to my new site. See you on the other side!

New discoveries - Heterodontosaurus

2009-08-24T04:55:00.000-07:00

Have a look at the cover of the latest newsletter of the PSSA (Palaeontological Society of South Africa). This is one of two new skulls of Heterodontosaurus that Billy De Klerk has found in the Elliot Formation of South Africa. It seems Billy is O.K. with showing them off to the world before he publishes on them, so I don't think there should be any problem with me posting this picture here. Things to note: the premaxilla fails to contact the lacrimal (a lacrimal-premaxilla contact was one of the proposed characters linking Heterodontosauridae to Ornithopoda)and the angular (ventral edge of the lower jaw) has a Yinlong-like rugose boss. There is a complete postcranium to go with this skull - so we can expect even more information on these rather wierd, early ornithischians in the nearish future.

Spongebob is a child of snowball Earth

2009-08-18T02:44:00.000-07:00

Image from commons.wikimedia.org

Although looking a little like plants, sponges (Phylum Porifera) are animals. Admittedly, they area very different kind of animal from the ones we see around us in everyday life. Unlike most others they lack bodies constructed from properly organized tissues, they are instead more like giant colonies of single cells. Indeed a famous experiment demonstrated that sponges that have been completely disaggregated into its constituent cells (by forcing them through a fine-mesh screen*) will begin to reconstitute themselves. Sponges lack any sort of gut, they instead live by sieving fine organic particles out of seawater. The food is absorbed directly by specialized ‘collar cells’ (more formally choanocytes) that line the canals and chambers that run through the sponges body. Sponges are also remarkable for their unique skeletons, which are generally made of tiny to microscopic spicules of silica or calcite or a lacy network of elastic organic material known as spongin (as in the original bath sponges). As you might expect with animals that lack a gut, nervous system or indeed organs of any sort, sponges are a very early branch of the animal tree. Indeed the tiny little disc of cells known as Trichoplax adhaerens may be the only living animal that branched away before sponges and all other animals split. Actually I’m oversimplifying here, because the evidence is looking good for sponge paraphyly. That means some of the different sponge groups are more closely related to tissue-grade animals (a clade called Eumetazoa) than to other sponges, so it wasn’t a single sponge-eumetazoan split. The remarkable conclusion that leads to is that we are directly descended from an animal that we would call a sponge.
Given their early divergence and simple construction, one would expect sponges to have a venerable fossil record. Indeed they do, but not quite as long as one might expect. Sponge spicules seemed to appear in the fossil record at the beginning of the Cambrian Period along with a great number of eumetazoan groups (now dated to 542 million years). Some spicules have been reported from older strata but these are not without controversy. In contrast eumetazoans clearly had an older fossil record (e.g. the 545-565 million year old Ediacaran fauna). The mid 1990’s saw the publication of Palaeophragmodictya, the first probable whole body fossils of sponges from the Ediacaran fauna. Nevertheless without spicular preservation (like other ediacaran macrofossils Palaeophragmodictya are preserved as impressions on the base of sandstone beds) there may always be some doubt as to its identity. What remains unusual is that it took so long for such Ediacaran sponges to be found and that they remain a very rare component of Ediacaran faunas.

Small individuals of the putative Ediacaran sponge Palaeophragmodictya. From Gehling and Rigby (1996)

Close up of a large Palaeophragmodictya showing what might be the impression of a spicular mesh.From Gehling and Rigby (1996)

Furthermore divergence dates calculated using molecular clock methods suggested a sponge- eumetazoan divergence of 650 million years. If the common ancestor was itself a sponge-grade organism we should expect the record of sponges and sponge-grade animals extending back to pre-Ediacaran times. This is well illustrated in the following diagram that teases apart the so-called ‘Cambrian explosion’(image from www.snowball.org). An interesting aspect of this molecular date is that it extends the range of animals back into a Period known as the Cryogenian, or just after it.

What is special about the Cryogenian? It was period in Earth history lasting from 750-620 million years where the Earth went through several severe glaciations events known as ‘snowball earths’. Although the exact severity of the snowball-earth glaciations is a contentious topic, there is convincing evidence that the Earth was cold enough to support sea-level glaciers in the equatorial belt. So an important question is: had animal divergence begun in the Cryogenian as the molecular divergence dates suggest? That question has been conclusively answered this year in a Nature paper by Gordon Love and colleagues.
Love et al. found convincing sponge fossils in sediments securely dated to the age of the Marinoan glaciation, the last snowball earth glaciations event of the Cryogenian. As a small aside the Marinoan is named after the seaside suburb of Marino, on the southern coast of Adelaide, my home town. My first ever geological field trip for my degree was looking at the Marinoan rocks of Marino. Anyway enough reminiscing, onto the Cryogenian sponges fossils. What were they? Spicules? Whole body impressions? No, Love et al. found molecular fossils, in particular 24-isopropylcholestanes. These particular hydrocarbons are, according to the authors, the degraded products of C30 sterols, a class of molecules only produced by members of the sponge class Demospongiae (here I have to accept the author’s word, I know far too little about organic chemistry to have any way of assessing the veracity of this statement). An interesting feature of snowball Earth Glaciations is that they are usually covered by a thin but continuous layer of carbonate rock: the 'cap carbonates'. These are thought to have precipitated out under extraordinarily hot conditions bought on by the retreat of the glaciers leaving behind an atmosphere dense in CO2 (which would accumulate while terrestrial weathering was essentially shut down underneath the ice-cover). Anyway these molecular sponge fossils are found in rocks below the cap carbonates, that is during the glacial period itself.
The implications are pretty huge. It means that multicellar animals arose and first diversified in frigid seas largely covered by ice, and not during the flush of warmth that suffused the planet immediately after the glaciers lost their grip. Where could animals exist in such a sea? There were probably numerous little oases of light where cracks in the relatively thin equatorial sea ice would allow local blooms of bacteria and algae. These little patches may well have been the birthplace of multicellular animal life.

A modern day equivalent of the oases that was the birthplace of animal life? Image from www.snowball.org.

References
Gehling, J.G. and Rigby, J.K. (1996) Long Expected Sponges from the Neoproterozoic Ediacara Fauna of South Australia. Journal of Paleontology 70: 185-195.

Love, G., Grosjean, E., Stalvies, C., Fike, D., Grotzinger, J., Bradley, A., Kelly, A., Bhatia, M., Meredith, W., Snape, C., Bowring, S., Condon, D., & Summons, R. (2009). Fossil steroids record the appearance of Demospongiae during the Cryogenian period Nature, 457 (7230), 718-721 DOI: 10.1038/nature07673

*They were the luckiest of all

Now is the winter of our fish content

2009-08-04T05:17:00.000-07:00

once again the dreaded lurgy has struck our family this winter with Anwen needing a stay in hospital. So this post and the next few to follow were supposed to be posted a month ago.

Teleost fish outnumber all other modern vertebrates two to one. Despite this staggering diversity it is accurate to call fish palaeontology the poor cousin of amniote palaeontology, particularly when it comes to grabbing publicity. Nevertheless with such a huge diversity it is not surprising that the clade has thrown up more than a few subgroups that do grab public attention. What is surprising is that the austral winter’s edition of Journal of Vertebrate Paleontology (volume 29, number 2) carries articles on no less than three of these attention grabbing teleost groups.
One is the giant ocean-going sunfish (Molidae). These giant jellyfish-suckers include the largest living bony fish but due to their poorly developed skeletons and pelagic habits have left a scrappy fossil record. Thus the finding of three articulated skeletons that exceed modern sunfish in size (one skeleton reaches 4 metres from fin tip to fin tip) is a big deal.
Another curious fossil fish reported in this issue is a deep-sea anglerfish (Ceratoidea). These bizarre fish are well known for their disproportionately large mouths lined with needle-like fangs and the ability attract prey with a luminescent lure. Finding a fossil of one of these is also quite unusual for the ceratoid clade is not all that old by geological standards. There simply aren’t that many places where such recent sediments have been laid down at great depth but have since been brought to a position above sea-level where someone might find any fossils that they might contain.
Both of these discoveries are blogworthy finds, however it is the fossil piranha that I want to highlight in this post (Cione et al. 2009). Piranhas are, of course, the fabled freshwater fish of South America that are said to be able to skeletonise a cow in a matter of minutes when a school is whipped up into a feeding frenzy.
The fossil piranha was found late Miocene (about 5 to 11 million years old) river sediments in northeastern Argentina. It has a concave dorsal margin of the premaxilla and tall, sharp triangular teeth that indicate that its affinities lie with the piranhas among the serrasalmids. Aptly named Megapiranha the fish is immediately striking for its great size. Known from a single jaw bone (the premaxilla) and some isolated teeth it is about two and a half times larger than the premaxilla of an average modern piranha. Assuming similar proportions to a modern piranha may have approached a meter in length.

A modern piranha against a silhouette scaled up to fit the size of the Megapiranha premaxilla.

Now the thought of a school of those getting into a feeding frenzy is worthy of any Hollywood B-grade creature feature. However it is far from certain that Megapiranha would have indulged in such hypercarnivorous behavior. It should be noted that piranhas form a clade of closely related species amongst a broader family of fish known as Serrasalmidae. Most serrasalmids (for example pacus) and even some piranhas are vegetarian, indicating that the herbivory is the ancestral diet of serrasalmids. Given the primitive position of Megapiranha (the sister group of all other known piranhas) it is quite likely that Megapiranha was at least partly vegetarian.
What makes Megapiranha interesting, other than its size, is that it gives us some idea how the piranhas evolved their famous dentition. Primitive herbivorous serrasalmids have seven rounded, flat-topped teeth arranged in two rows. In contrast piranhas have a single row of six double-cusped, blade-like teeth. One would expect that the single rowed condition evolved from the double rowed condition by simple suppression of one of the rows, most likely the inner row which contains just two teeth. An alternative, proposed by Gosline (1951) is that the two rows integrated to become one. Megapiranha provides evidence that supports Gosline’s hypothesis, for it shows just a single tooth row but with the teeth placed in a staggered arrangement as if two rows were merging.

The premaxillae of a pacu (top), Megapiranha (middle), and a modern piranha (bottom)in lateral (left) and ventral (right) views. Scale bars equal 1 cm. Images from Cione et al. 2009.

The teeth themselves are intermediate as well for although they bear tall, sharp-edged triangular cusps like modern piranhas, there is no secondary cusp and the bases are broad, perhaps supporting the idea that Megapiranha was not a hypercarnivore. It is a pity really, I find the idea of a giant ground sloth or an astrapothere being stripped to its bones by a school of meter-long piranhas somehow appealing.

References

Cione, A.L., Dahdul, W.M., Lundberg, J.G. & Machado-Allison, A.(2009) Megapiranha paranensis, a new genus and species of Serrasalmidae (Characiformes, Teleostei) from the upper Miocene of Argentina. Journal of Vertebrate Paleontology 29: 350-358.

Gosline, W. (1951) Notes on the Characid fishes of the subfamily Serrasalminae.
Proceedings of the California Academy of Sciences 27: 17–64.

Three New Dinosaurs - at long last, some dinosaury goodness from Australia

2009-07-05T23:25:00.000-07:00

Three new Australian dinosaurs, Australovenator wintonensis at the top, Wintonotitan wattsi in the middle and Diamantinasaurus matildae below. Scale bar equals 1 metre. From Hocknull et al. 2009.

What a year for dinosaur research it has been. We’ve had: the publication of a Cretaceous heterodontosaurid with filamentous integument; a slew of new taxa including a member of the perennially popular tyrannosauroids; a toothless, herbivorous ceratosaur !!! with a bizarre hand (which may or may not shed light on the homology of bird fingers). Now that dinosaur depauperate continent , Australia, that produced naught but a handful of decent dinosaur fossils in all the years I lived there, has thrown up three new taxa. The open access paper is here.
Aussie geo-folklore would lay the blame on its apparent dinosaurlessness on the geological quiescence Australia has experienced since the Mesozoic. With no major mountain building events to thrust up strata of the right age there is very little exposure to search and much of that has just been sitting around since it was deposited getting ever more deeply weathered.
While much of this is true it does not preclude the preservation and excavation of decent dinosaur fossils as this new paper shows. The fossils come from the cattle country of central Queensland. Where the land is as flat as a tack, and almost completely grassed over. Not exactly promising territory for palaeontological exploration. Nevertheless the area is unlerlain by the Winton Formation an sedimentary unit laid down on a floodplain fringing a great epicontinental (‘inland’) sea during the middle part of the Creataceous Period.
So why not dig down to the sediments? That is exactly what the team reporting (Hocknull et al.) these new dinosaurs has done. According to the pHocknull et al. the subcrop of the Winton Formation lay under just 1 m of overlying soil. We’ve cut through thicker piles of overburden in our Elliot Formation, so it is not that the Winton Formation is out of reach. Of course, on such flat soil covered land you are lacking the usual clues like fragments of weathered bone falling downslope to lead you to productive sites, nonetheless chunks of weathered bone in the soil can signal something worthwhile lies below. Furthermore the excellent state of preservation of some of these bones (particularly those of the theropod, Australovenator) show that deep weathering profiles may not be quite the problem they’ve been made out to be.
So what did Hocknull et al. find? Two new sauropods (Wintonotitan wattsi and Diamantinasaurus matildae, both titanosauriforms, and an allosaurid theropod (Australovenator wintonensis). Actually to say that two new sauropods were found is not strictly accurate. The holotype specimen of Wintonotitan had been found decades earlier, described as Austrosaurus sp. (Coombs and Molnar 1981) and even incorporated into a phylogenetic analysis of sauropod relationships (as Austrosaurus, Upchurch et al 2004). The type of Austrosaurus is just a series of beat-up dorsal vertebrae, consisting mostly of the centra alone. It comes from the slightly older Allaru Mudstone and differs slightly from the dorsal vertebra of Wintonotitan, indicating that the two are not synonyms. In anycase the name Austrosaurus is best dropped as a nomen dubium based on inadequate remains. A couple of rather preliminary phylogenetic analysis suggest that both sauropods are somphospondyls (titanosauriforms more closely related to ‘classic’ titanosaurs (exemplified by the armoured Saltasaurus from Argentina) than to Brachiosaurus. This is an unsurprising result as almost all sauropods of this age belong to this group. Wintonotitan was found to be a relatively basal member of the group, outside the Titanosauria proper but certain features such as the plate-like ischium with elongate iliac peduncle, medially shifted deltopectoral crest on the humerus and the eye-shaped pleurocoels in the dorsal vertebrae indicate that Wintonotitan may actually hold more derived position within Titanosauria, like its compatriot Diamantinasaurus.
Anyway it is the carnivore, Australovenator that I want to discuss for the rest of this post. As Hocknull et al. point out the non-avian theropod record from Australia is abysmal so there is little to compare it too. One recently described Australian theropod is NMV P186076, an isolated ulna from the Cretaceous of Dinosaur Cove, Victoria that Smith et al. (2008) found to be closely related to the large tetanuran Megaraptor from Argentina. While Hocknull et al. point out some differences between the ulna of Australovenator and NMV P186076 they don’t make much of the strong similarities that these ulnae display in comparison with other basal tetanuran theropods. These similarities include an hypertrophied, mediolaterally compressed olecranon process and an enlarged, proxiodistally elongated lateral tuberosity, defining a cranial fossa. You can see the similarity in the composite figure I whipped up below.

Ulnae of Australovenator and cf. Megaraptor from Dinosaur Cove. Lateral view on left anterior vie in the middle and proximal (top) view on the right. The larger pale brown bone is Australovenator the smaller dark grey bone is cf. Megaraptor.

A ‘megaraptorid’ identification for Australovenator also gels with its rather large wicked looking thumb claw that is about three times longer than its proximal height. More interesting is the astragalus (main ankle bone) of Australovenator which bears a striking resemblance to another isolated Victorian bone, this time from the Cretaceous deposits near Inverloch, which has been touted as everything from Allosaurus to an abelisaurid. Thus despite the small time gap between the two isolated Victorian theropod bones it is quite possible they came from closely related animals. That three separate occurrences from the middle of the Cretaceous of Australia seem referable to this clade indicates to me that these ‘megaraptorids’ were the dominant large carnivores in the middle Cretaceous of Australia.
‘Megaraptorids’ (if indeed they are a clade) are still rather fragmentarily represented, so the addition of Australovenator is most welcome. It helps pull in some other poorly known theropods into this newly recognized fold. One of these is Fukuiraptor kitadanensis a small possible allosauroid from Japan, that has an astragalus that closely resembles the astragalus from Inverloch and that of Australovenator. Although damaged the ulna also appears to bear an unusually large mediolaterally compressed olecranon process. Chilantaisaurus tashuikouensis is a second possible ‘megaraptorid’ from the Cretaceous of Asia. Last year when Smith et al. published the Dinosaur Cove ulna I suggested that this giant asian theropod was a megaraptorid based on: 1, the enlarged manual ungual 2, an apparent close relationship to spinosaurids found by Rauhut (2003)and 3, a similar position for ‘megaraptorids’ found by Smith et al. (2008). Although the spinosauroid position for ‘megaraptorids’ is looking weaker than their position as a basal radiation of carcharodontosaurid allosauroids, I still think there may be a possibility that Chilantaisaurus is a megaraptorid. Supporting this is the presence of a distal craniomedial ridge of the tibia in Australovenator much like the ridge seen in Chilantaisaurus (admittedly this ridge is also found in Suchomimus and Coelurus, so it is not unique to ‘megaraptorids’). Adding a little strength to this idea is the rather hatchet-like deltopectoral crest of Fukuiraptor which looks like a partially developed version of the strongly hatchet-shaped deltopectoral crest of Chilantaisaurus.
In conclusion the ‘megaraptorids’ might be a cosmopolitan clade of Cretaceous allosauroids that share a hatchet-shaped deltopectoral crest, an unusual ulna morphology with an enlarged, blade-shaped olecranon process, an enlarged thumb claw, a femoral head that is not as strongly elevated as other known carcharodontosaurids, a medial ridge on the distal tibia and a distinctive astragalus with a square shaped ascending process. If this clade really exists we can expect earlier representatives to extend back into the Jurassic to allow them to have achieved their near cosmospolitan distribution. Time, new fossils and further analysis may tell.

References.

Coombs WP Jr., Molnar RE (1981) Sauropoda (Reptilia, Saurischia) from the Cretaceous of Queensland. Memoirs of the Queensland Museum 20: 351-373.

Hocknull, S., White, M., Tischler, T., Cook, A., Calleja, N., Sloan, T., & Elliott, D. (2009). New Mid-Cretaceous (Latest Albian) Dinosaurs from Winton, Queensland, Australia PLoS ONE, 4 (7) DOI: 10.1371/journal.pone.0006190

Rauhut OWM (2003) The interrelationships and evolution of basal theropod dinosaurs. Special Papers in Palaeontology 69: 1-213.

Smith ND, Makovicky PJ, Agnolin FL, Ezcurra MD, Pais DF and Salisbury SW (2008) A Megaraptor -like theropod (Dinosauria: Tetanurae) in Australia: support for faunal exchange across eastern and western Gondwana in the Mid-Cretaceous. Proceedings of the Royal Society B: doi:10.1098/rspb.2008.0504

Upchurch P, Barrett PM and Dodson P (2004) Sauropoda.Pp. 259-322. In Weishampel DB, Dodson P and Osmolska H (eds) The Dinosauria. Second Edition.University of California Press: Berkeley.

Another squamate post - Acontias gracilicauda

2009-07-02T00:12:00.000-07:00

Photos by Matt Bonnan

No time for an in depth post today, so I'm keeping the squamate theme going with a picture from my archives. This is a legless skink (Acontias gracilicauda)that happened to have made it home directly above an early Jurassic sauropod bone bed. So it had to be relocated. There is a moderate diversity of acontine skinks in southern Africa: they are just one of many lizard lineages, apart from snakes, that have beome completely limbless.

Happiness is a bucket of lizards

2009-06-29T05:44:00.000-07:00

One of the aspects of academic life in a small research institute is that you are sometimes called upon to supervise student projects that are outside your normal sphere of research activities. Broadening your experience and knowledge can only be a good thing so I welcome this. It also can provide an outlet of unusual activities that can break the monotony of the usual working week.
I am currently supervising one such project that is proving to be quite entertaining. The project is centred upon the almost entirely neglected herpetofauna that occurs alongside the famous Australopithecus fossils of the Cradle of Humankind World Heritage Area.
I found out, much to my surprise, when this project was started that there are no comparative osteological collections of southern african reptiles available in South Africa. So we have had to set about creating one. Fortunately we have been given permission to prepare the skulls of duplicate specimens from the Transvaal Museum collections. I was very pleasantly surprised at the breadth of the taxonomic scope we were supplied with - two specimens of over 40 species from the eastern half of
South Africa. So it was with some excitment that we took consignment of the above pictured and rather full bucket of lizards (Can anyone name the species visible? I'd be impressed if someone managed five or more).
Of course it is the students job to prepare the skulls, but with so many to get through, I've been mucking in and helping with the defleshing, which is surprising satisfying work, especially when you finish with a nice clean skull.

Early Jurassic side-winder - but is it a snake?

2009-06-22T06:12:00.000-07:00

Francois Durand's side-winding trace from the Clarens Formation. From Durand (2005.

Discussion about fossil side-winding traces over at Tet Zoo prompted me to get off my butt and actually put something up on this blog.
Its Francois Durand's apparent side-winding trace from the Clarens Formation of South Africa. Not much has been made of this and the only two references to it that I know of are rather obscure so I'm putting it up here to let people know about it.
It certainly looks like a track left by a modern sidewinding viper.

A modern side-winder

Francois made it fairly clear in his presentation of this fossil to the Geoscience Africa conferance back in 2004 that he thought it was made by an Early Jurassic viperid although he only hints at this in the two publications featuring this fossil that I know of. Such an occurence is strongly at odds with the known fossil record of snakes. Even the most primitive snakes don't show up until the Cretaceous, and advanced snakes like viperids don't start radiating until well in the Cenozoic, thus to have a Jurassic Viperid means that just about all tradtional family level clades of snakes have massive ghost lineages stretching back tens of millions of years. The fossil record can be spotty but it ain't THAT bad.
My take is that sidewinding habit may have evolved sporadically from time to time in all sorts of elongate limb-reduced tetrapods when the conditions warranted it. The whole discussion started over the possible sidewinding traces from a Permian, wet muddy, if not aquatic environment that I had a hand in describing.If correctly interpreted sidewinding need not be restrited to dry loose sand, wet sloppy mud might be just as capable of supporting it.
So what was elongate sidewinding tetrapod of the Clarens? We haven't a clue.

references

Durand, J.F. 2004. The origin of snakes. Geoscience Africa 2004. Abstract Volume, University of the Witwatersrand, Johannesburg, South Africa, pp. 187.

Durand, J.F. 2005. Major African contributions to Palaeozoic and Mesozoic
vertebrate palaeontology. Journal of African Earth Sciences 43: 53-82.

So how did it go?

2009-05-29T04:31:00.000-07:00

The interview turned out to be quite long after all, and rather enjoyable, although these type of things always make me nervous. We were a panel of three: a catholic preist (whose name I didn't catch due to my hyped up state before the interview)and Jens Franzen, the lead author on the Darwinius paper. Straight off the bat the religious aspect was deflated by the priest stating categorically that the church accepted evolution as the correct mechanistic explanation for the diversity of life and that this was an unguided naturalistic process (I must admit I was surprised to hear a member of the clergy accepting an unguided evolutionary process), as long as god was the creator of the whole show. I was then asked whether or not Darwinius was 'the missing link' urggh! So I attacked the idea of 'missing links' as a valuable concept at all and explained that Darwinius was a primate, like us, but simultaneously quite ancient and distant from us as far as primates go. Towards the end of my little speech I mentioned that its real significance was that it may have been a bit more closely related to anthropoids (monkeys, apes and humans) than to lemurs and thus may have been a very early member of the haplorhine branch of the primate family tree. I was quite equivocal about wether this was a firmly established scientific case. This may have antagonised Jens Franzen a little who went into quite a long discussion about why it was a haplorhine and not a lemur relative. The interview was rapidly in danger of becoming much like a technical question and answer session at a palaeontological conference (mores the pity that it didn't) so the topic was changed and Jens was asked many things about the discovery of Darwinius and its dating. This part of the interview was very informative. Of course the produces wanted more of the religion angle so we were asked our opinion of 'intelligent design'. The prist denounced it saying that it required an intervenionist god to create each lifeform sepparately which is flatly at odds with the evidence. I joined in with some fairly scathing remarks along the lines that it was a scam cooked up by the young earth creationists to get their particular narrow literal biblical interpretation taught as science in American schools. It of course isn't science and it failed in court.
And that is about it. I was told afterwards by several people that I came across clearly and confidently - which is great because I certainly didn't feel it.

UPDATE. Yes there is an MP3, you can download it from here.
I need to say three things here. 1) The preist was Father Anthony Egan - my apologies for not remembering.
2) My voice is not so clear, probably because I was on a cell phone at home.
3) the faint cries heard in the background was Matthew, who decided he wanted milk urgently, sometime during the middle of the interview.

Radio Interview

2009-05-27T04:59:00.000-07:00

For those of you in South Africa* - I'll be interviewed on classic FM at 7.30 tonight. Apparently they want a palaeontologist's opinion on the religious implications of Ida, the new fossil primate that everyones all het up about. Religious implications?! There AREN'T ANY! Should be a short interview.

*huh! who am I trying to kid, I'm sure I have no readers left at all after the long dark silence that has descended over my blog

Organisms I Hate: Khaki Bush

2009-05-18T00:26:00.000-07:00

Allow me to vent my spleen a little. Although I revel in biodiversity and am fascinated by so many orgnaisms there are some I just plain hate. This is one of them. Khaki bush/mexican marigold (Tagetes minuta)- an unpleasant stinking weed that grows profusely where-ever I need to do field work in South Africa. These tenaciously sticky seeds come off from the seed heads at the slightest touch and embed themselves in any form of clothing. After walking through a field of these you can end up looking like you are covered in black spiky fur.

This was what I bought me out into the field over the weekend - a partial dinosaur skeleton from an odd mudstone lens way up in the Clarens Formation, where dinosaurs are rare. Somewhat disappointingly it turned out to be just another basal sauropodomorph. Oh well.

Finding a fossil and filling a gap: The story of Lyncina onkastoma Yates, 2009

2009-04-07T07:14:00.000-07:00

February saw the release of my second paper on the fossil cowry shells of Australia. This one is potentially more interesting for it deals with some of the oldest fossils of this group in Australia and thus sheds some light (admittedly not too much) on the somewhat mysterious origins of the southern Australian endemics.

The modern Australian cowrie fauna is divisible into two great provinces: Those from the north and those from the south. The tropical northern fauna is just a subset of the tropical indopacific fauna and displays little in the way of endemicity. In the south however we have a range of distinctive clades that are endemic to the region. Each of these clades have been given their own genus name: Umbilia, Zoila, Austrocypraea (now a subgenus of Lyncina) and Notocypraea. Notoluponia is a fifth endemic southern Australian cowrie clade but is unfortunately extinct. Phylogenetic analysis has shown that these lineages are not each others closest relatives amongst cowries but each shares relationships with other non-Australian cowrie groups. When did these lineages arrive in Australia and where did they come from? These apparently simple questions are quite difficult to answer. Firstly the fossil record of cowries in Australia is almost entirely restricted to the last half of the Cenozoic. Until recently the oldest cowries did not appear until right at the end of the Oligocene Epoch (about 23 million years ago) whereas the cowrie elsewhere in the world cowries belonging to modern genera can be found back as far as the Eocene and other cowries go back into the Cretaceous. What is more the oldest cowries Australian endemic cowries were clearly members of the endemic lineages and betray little of their origins. Why is this so? Perhaps cowries enterered southern Australia during the early Oligocene. This represents a ‘black hole’ in our record of molluscs in Southern Australia. We have good molluscan faunas from the late Eocene (about 35 million years old) but virtually nothing in the 12 million years or so between these and the late Oligocene appearances. Nor are there any well-preserved molluscan assemblage that fill this gap. Do we just give up at this point?
Of course not. The glaring gap in our knowledge is the result of various workers almost entirely ignoring molluscs preserved as moulds and casts, in favour of those with the original shell preserved. It is true that an original shell is a much easier object to study than a series of moulds and casts (and can be an object of great natural beauty) but if moulds and casts is all you’ve got, shouldn’t we be looking at them?

Enter the Port Willunga Formation. This is a marine unit exposed on the coast of Fleurieu Peninsula, South Australia that dates from right in the middle of that ‘black hole’ in our knowledge of molluscan faunas. It is too porous to preserve mollusc shells but moulds and casts can be found if you look in the right places. This is one of the right places:

Limestone cliffs and shorecut platform just south of the mouth of the Onkaparinga River. Image used with the kind permission of Glenn Alderson. You can see more of Glenn’s pictures here.

Isn’t it beautiful? The Fleurieu coast is full of wonderful little beaches like this one. Apart from fantastic swimming, snorkeling and diving they also have fossils! Wow, who could ask for more? So when spending time with my family in Adelaide I always try to get down to some of the nearby fossil sites.
Late one afternoon when returning from further afield, my father and I stopped off at this beach (precisely for the reason of seeing if mollusc moulds and casts were preserved in the mid Oligocene rocks that crop out there). While wandering around on the rocks I happened to look down and noticed what appeared to be a cowrie internal mould sitting in its external mould. I got pretty excited straight away for I knew this was amongst the oldest known cowrie fossils found in Australia and might belong to a primitive stem-form of one of our endemic lineages. It may not be in the same league as Tiktaalik but it is nice when you set out to find something in palaeontology and you find it exactly where you were predicting it to be. The image below is actually a little volute from the same site – it gives you an idea of how unprepossessing these fossils are in the field.
Nevertheless if you collect the external mould and carefully chip as much of the apertural impression as you can away from the internal mould and glue it to the external mould, you can then take a pretty decent latex peel. This is what I did for my cowrie and this is the result.

I went back to the site two days later and found a further four specimens although none were quite as good as the first which subsequently became the holotype specimen of Lyncina (Austrocypraea) onkastoma.
It is indeed a very early member of one of our endemic lineages: Austrocypraea which I’ve talked about before on this blog. However it is a rather odd Austrocypraea, most noticeably because its fossula (see primer on cowrie shell anatomy here) is smooth and its apertural teeth are short, weak and confined to the anterior end of the shell. Such features are derived among members of Lyncina but are shared to some extent with L. (A.) archeri, the next oldest known member of L. (Austrocypraea). L. (A.) archeri dates to the earliest Miocene Epoch (about 22 million years old) and would appear to be a close relative of L. (A.) onkastoma. If these two early Austrocypraea form a clade diagnosed by specializations not seen in later Austrocypraea, or indeed any other members of the wider Lyncina clade, then it suggests that some diversification had already gone on by the early Oligocene (the age of L. (A.) onkastoma) and that we can expect to find more cowrie species in the Oligocene of South Australia – if only we take the time to look.

Yates, A.M. (2009) The oldest South Australian cowries (Gastropoda: Cypraeidae) from the Paleogene of the St Vincent Basin. Alcheringa 33, 23-31.

Access Denied! When ignorance stops science

2009-03-30T05:02:00.000-07:00

I've been back from my field trip for exactly a week now, but I simply haven't found time to blog at all. The field crew was a large one and juggling the group was logistically difficult - especially in the face of having to make up new plans on the spot, when the old ones fell through. What went wrong? I'll tell you.
The trip was originally planned to continue work began last year by a joint Wits - BSP (Munich) expedition with a small contingent (Richard Butler) from the NHM (London). This trip began exploration and collection in the historically rich Herschel district of what is now the Eastern Cape. As a breif primer it was this district that produced the holotypes of Melanorosaurus readi, Plateosauravus cullingworthi, Heterodontosaurus tucki, Blikanasaurus cromptoni and Stormbergia dangershoeki as well as a some of the best specimens of Massospondylus carinatus and the spectacular complete skeleton of Heterodontosaurus (not the holotype).
Politically the area is a difficult one to work in because historically it was an isolated fragment of the Transkei, a 'homeland' for black south africans - not to dissimilar to Indian reservations in the US. Although integrated with South Africa in 1994, the Herschel district has remained in dire poverty and partly under the old governance of cheifs and big men. The national government has however set up wards and councillors who are supposed to work together with the traditional rulers.
It was some trepidation that our team stepped into this region, with the view of exploring this territory. One of our goals was placing new positively associated and identified dinosaur specimens on accurately measured strat sections to better understand dinosaur distributions through the Elliot. We also just wanted to see what else we could find to flesh out the fauna of the Elliot - many taxa are still known from single specimens and new discoveries are made often enough to indicate that the discovery curve for the Elliot is not yet near a plateau.
We decided that Blikana Mountain - magnificent area of near continuous outcrop would form the basis of our search effort. After contacting the local councillor responsible for Blikana and meeting with her we were granted permission to explore and excavate.
Although the region has a fearsome reputation we found the locals friendly, somewhat bemused by our interest in stones and eager to help. Many knew about fossilised bones and told us about likely sites.
Thus when we returned this year we were hoping this good relationship would continue. Alas it was not so.
Immediately upon arrival we knew something was up. We had to meet with the councillor in town and under no circumstances set foot on Blikana. It turns out that the councillor was not going to grant us access because she claimed some residents of the area thought we were digging up the bones of their forefathers and robbing their graves and she supported their concerns. It seems the problem started when we showed the councillor herself some of the dinosaur bones we were looking for and gave them to the local school for educational purposes (isolated surface bones are generally abundant). This part of South Africa must be one of the very few places on Earth where the general population has never heard of dinosaurs. Sadly the councillor was unwilling to listen to our explanation that these bones predated any human and were certainly not hers or anyone elses ancestors. Reason didn't seem to work when we pointed out that these bones patently couldn't even fit inside a human body. I suspect that there was more to the problem than was being stated, perhaps we were a difficult problem and the councillor simply wished us to go away. Afterall the elections are near, there has been a split in the ruling party and tensions are running high. No politician wishes to stick their neck out at times like these. Another argument levelled at us was that we were giving no benefit to the locals. Here we are fighting an insidious meme that unfortunately has deep roots in South Africa, that is science = colonial imperialism. Sadly we could not convince her that our science uncovered important natural heritage for all South Africans, indeed all people of the world to share.
In anycase the exposures of the Elliot Formation are simply too good to ignore (they are the best in South Africa), it seems we will have to embark on a campaign to raise local awareness of the important natural heritage that lies beneath their feet.

Off into the field

2009-03-05T05:22:00.001-08:00

Its a mad mad world at the moment. I'm currently preparing for a big field trip into the wild yonder of the Eastern Cape with a team from the Bayerische Staatssammlung für Paläontologie und Geologie, Munich and the Natural History Museum London. I'd love to blog about: Basal theropods with bird like hand postures; my second paper dealing with the fossil cowrie fauna of South Australia; the non-existance of Ward and Smith's single Permo-Triassic event bed in the Karoo Basin; or any number of other things. But I just don't have the time or the energy right now. So things are going to be real quiet here until I get back from the field (hopefully laden with fantastic new dinosaur specimens that I would unfortunately not be able to you about anyway until they were published....sigh.

stegopod!

2009-02-25T23:36:00.000-08:00

Photo (Octavio Mateus) and reconstruction (from the paper) of the new stegosaur Miragaia longicollum.

Once again I'm late to the party. Miragaia longicollum is the newly published, long-necked sauropod mimicing stegosaur from the Late Jurassic of Portugal that was featured in loads of blogs yesterday. Attendees of the SVP annual meeting may have actually caught the reconstruction of Miragaia way back in 2007, in Austin. Even though it was only up on screen for a short time, the crazy long neck was immediately obvious, and I've been waiting for it to be published ever since.

Ayway neck elongation in this stegosaur was covered very well by Matt Wedel here. So I won't spend anymore words on it here. Instead I'll delve into the systematics of Miragaia. At the outset let me say that I think the authors have done a great job in this paper and they are thoroughly deserve the publicity they are getting. However this one lttle niggly aspect of the paper has not convinced me and I want to raise the issue here because the fault seems to lie with the whole culture of publication in palaeontology, rather than with these specific authors.

First off Miragaia shares a bunch of characters with the roughly co-eval English stegosaur, Dacenturus. These include fusion of the cervical vertebra to their respective centra, dorsal vertebral centra that are wider than long and olecranon process of the ulna developed into a horn-like prong (you can see this last feature clearly in the photo above). Indeed when the two are included in a cladistic analysis the two form a well supported clade which the Mateus et al. call the Dacenturinae. Another interesting tidbit is that the new data from Miragaia shifts Dacenturus from its usual basal position amongst stegosaurids to a derived position next to Stegosaurus itself. Interestingly though when Mateus showcased this skeleton in 2007 he had identified it AS Dacenturus.
So what makes Miragaia distinct? Obviously its unusually high number of neck vertebrae is a wierd feature (and there are several others listed in the diagnosis) but this cannot be determined in Dacenturus because it is mostly known from the backend of the animal while Miragaia is largely known from the front.

Indeed due to this non-overlapping parts problem just about all of the autapomorphies of Miragaia are not determinable in Dacenturus. So is there a justification for erecting a new taxon? I went through the character taxon matrix in the supplemental material in order to find out if there was any observable differenceand found a few points of difference. All but one f these concerned the continuously variable characters (e.g. ratio of distal width of the humerus to its length)and in most cases the difference was slight so that in more traditional discrete character state coding these features might be given the same state. The one discrete character difference in the matrix concerned the robustness of the dorsal plates but once again the known plates of Miragaia are from the front of the animal while those known from Dacenturus come from further back so we may not be compareing the same thing.

In all there seems justification for at most a new species of Dacenturus (especially since its sister taxon Stegosaurus, houses three species which display more disparity than these two genera). Maybe I'm missing something but f so the authors really could have made the distinction between these two genera clearer.

Does erecting a new taxon make publishing a new fossil easier? It shouldn't, the Miragaia fossils are fantastic enough to deserve publication in the Proceedings. But nonetheless I have heard talk that editors of these high-impact broad science journals are less keen to publish palaeontology if it doesn't involve a new taxon. If this is so, and I hope it isn't, then it is a practice that has to stop, an important fossil that throws new light on evolution or palaeobiology deserves recognition wether or not it represents a new taxon.

Mateus, O., Maidment, S. C. R., Christiansen, N. A. (2009). A new long-necked ‘sauropod-mimic’ stegosaur
and the evolution of the plated dinosaurs Proceedings of the Royal Society B DOI: 10.1098/rspb.2008.1909

Egg Eating Snake

2009-02-23T23:30:00.001-08:00

Moving to a new continent is a simulataneous joy and frustration for those with a naturalist bent. On the plus side there is a whole new fauna and flora to discover. On the downside until you become very familiar with it you often haven't got a clue what you find is. This happened to me on a recent short field trip to Golden Gate Highlands National Park. The trip was a total washout, heavy rains and bad weather made it unpleasant in the field and had caused a rockfall that obscured much of the site we wanted to investigate. However while scrabbling around the rockfall I found this beautifull little snake. I didn't know it at the time but I had found a rhombic egg-eater (Dasypeltis scabra), a member of a fascinating group of snakes I had always wanted to see. Sadly I thought it was a night adder so treated it cautiously I didn't give it a very close look. Night adders are quite venemous whereas egg eaters are virtually toothless and quite harmless (unless you happen to be a small bird egg). Only later when I was back home did I identify what it really was.

A little about Dasypeltis snakes for those who don't know. They are an african genus of colubrids that are adapted to feeding exclusively on bird eggs. They are capable of swallowing eggs up to three times the width of their head. They have highly reduced dentitions and use ventral projections from the vertebrae in the gullet region to pierce the shell. The liquid contents are swallowed and the collapsed shell is regurgitated. I would love to see this in action, but my little guy was just sheltering from the bad weather when I found him.

Fossil Human Hair

2009-02-18T02:59:00.000-08:00

200 000 year old human hair from a hyaena coprolite. Image from Backwell et al. 2009

Over a week ago Lucinda Backwell, who also works at the BPI at Wits, announced the discovery of fossilised human hair that exceeds the previous oldest known hair (from a 9000 year old mummy) by about 200 000 years. Indeed it is so old it might not even belong to our own species but might instead belong to H. heidelbergensis.
The story was picked up by some of our local papers but doesn't appear to have generated much interest in the blogosphere, so I thought I'd timidly foray into the world of palaeoanthropology and discuss Backwell et al.'s paper here.
What adds some iterest to the story is where the fossil hair was found: inside a hyaena coprolite from Gladysvale Cave in the 'Cradle of Humankind' , South Africa (practically next door to such famous sites as Sterkfontein and Swartkrans). Coprolites are, of course fossilised faeces.
Does this mean a hyaena attacked and killed a Homo species in the Late Pleistocene of South Africa? Well I'm sure our ancestors and relatives may have on occasion fallen prey to spotted hyaenas and some of the larger extinct forms. However this fossil does not record such an event. The coprolite was part of a latrine buried in situ in Gladysvale Cave,and the details of this latrine, such as its location inside a cave, small size and well circumscribed boundaries, all indicate that it was made by a brown hyaena (Parahyaena brunnea). Brown hyaenas are rather smallish and are not known to kill humans. Far more likely is that this represents scavenging on an already deceased member of our genus.

A brown hyaena

It was the cave setting that allowed the latrine to be dated. The latrine is sandwiched between two flowstones which contain enough Uranium to be used for Uranium-Thorium dating. This dating was done as part of a larger project by Robyn Pickering, one of the brightest students to come through the BPI in recent years.
Sadly the hairs are preserved as casts in carbonate. No trace of organics are left so we won't be getting any molecular data for 200 000 year old hominids just yet.
By itself that is about all that the paper can tell us. Perhaps if more such latrines could be found we could then survey more scats for fossil hair and discover how frequent such scavenging events occured. Discovery of even older hair, might start to reveal systematic variation and we might even be able to hazard some guesses as to what kind of hairs our more remote relatives bore. For instance we might be able to get a handle on when modern style short fine body hair evolved. The Gladysvale deposits cetainly go back much further in time so the potential for finding australopithecine hair is there.
This also serves to remind us that coprolites are unique microenvironments that have unusual preservation potentials. Ever snce the oldest known mammalian hair was found in Paleocene coprolites, I've thought that coprolites offer us the best chance to find out just when our unique mammalian pelage evolved. I have looked through coprolites from a Middle Triassic synapsid bearing site in the hopes of finding non-mammalian hair but so far no luck.

UPDATE: Randy rightly asked how the ID was made. Mammalian hair is not completely diagnostic to low taxonomic categories. It helped that several specimens were found in the coprolite. Any one hyaena scat usually contains the hair from just one sitting so is not likely to be mixed with other species. Thus there was a sample of several hairs to work from. Only human hairs were found to match the range of variation seen in the fossil hairs (using characteristics such as scale margins, scale spacing, hair width etc.). Other primates came close but most non-human primates produce finer hair. So the ID is a probabilistic one, hence the equivocation in the title of the paper.

L BACKWELL, R PICKERING, D BROTHWELL, L BERGER, M WITCOMB, D MARTILL, K PENKMAN, A WILSON (2009). Probable human hair found in a fossil hyaena coprolite from Gladysvale cave, South Africa. Journal of Archaeological Science DOI: 10.1016/j.jas.2009.01.023

Before they were giants, a new fossil from the dawn of the age of dinosaurs

2009-02-17T02:49:00.000-08:00

I was shut off from the internet all this morning. When I got back online I find the wonderfull news that a brand new dinosaur from Argentina has been described by Ricardo Martinez and Oscar Alcober. And not just any dinosaur, a basal sauropodomorph, indeed THE basal sauropodomorph. How could I not blog about it?
Called Panphagia protos (meaning 'the first that eats all' - a reference to its basal position and probable omnivory) it hails from the Ischigualasto Formation. The authors give its age as the earliest Carnian but this is actually not likely given the shake up that Triassic dating and stratigraphy has been getting over the last few years. The revised stratigraphy puts the Ischigualasto right at the very end of the Carnian and probably extending into the earliest Norian.
In anycase Panphagia is a much more primitive sauropodomorph than anything else described so far including the equivalent aged Saturnalia from Brazil. It doesn't have reduced skull and the neck is barely elongated relative to the neck of basal theropods (this depends on wether or not you include herrerasaurids and Eoraptor among the theropods).
However it does show a handfull of rather subtle sauropodomorph features including an enlarged external naris (also in Eoraptor), basally constricted tooth crowns (also in some teeth of Eoraptor) and a non-articulating gap between the transverse processes of the first sacral vertebra and the ilium in the pelvis. The authors cite a few other characters but none are overwhelmingly convincing. And this is the point. We are dealing with the very roots of the saurischian dinosaur radiation and the different lineages had not yet changed enough to accrue distictive characters to convincingly diagnose them. Indeed the similarity between Panphagia and the contemporary dinosaur Eoraptor (which some claim is the basalmost theropod) is very strong, a point not lost on the authors. If I read the subtext of the article correctly I think the authors are hinting at the possibility that Eoraptor is also a basal sauropodomorph. I have certainly entertained the idea in the past but unfortunately I've never seen the Eoraptor fossils and published details are frustratingly sparse so I cannot claim to have an informed opinion.
How did Panphagia make a living? It was certainly not a full time herbivore, nonetheless its somewhat leaf-shaped, imbricated teeth are not quite the slashing deadly blades weilded by its herrerasaurid and rauisuchian contemporaries. Martinez and Alcober are clearly in favour of an omnivorous diet and I concur. Looking at the jaw I can easily imagine such a set of teeth catch and slicing up small time prey while also shredding soft nutritious vegetable matter (e.g. new shoots and fleshy reproductive structures).

All purpose teeth of Panphagia from Martinez and Alcober 2009

To sum up, the morphology of Panphagia actually presents no real surprises, its pretty much exactly what I would have suspected the earliest of sauropodomorphs to have looked like (is this a sign that we are on the right track and our phylogenies are a pretty accurate reflection of dinosaur evolution?). The bigger surprise s its age. Since there is a more advanced sauropodomorph of similar age (Saturnalia) I wonder wether the survival of the less specialised Panphagia alongside it might just be hinting that the initial radiation wasn't that much older. Put more simply the initial divergence of theropods from sauropodomorphs, and indeed saurischian dinosaurs from ornithischian dinosaurs may have only occured during the Carnian Stage of the Late Triassic, rather than extending back into the Middle Triassic as is often postulated.

Ricardo N. Martinez, Oscar A. Alcober (2009). A Basal Sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the Early Evolution of Sauropodomorpha PLoS ONE, 4 (2) DOI: 10.1371/journal.pone.0004397

Bushfire Tragedy

2009-02-09T05:38:00.000-08:00

In these days of instant news from around the globe, the horrible tragedies that strike at humans everywhere start to wash over you without the horror truly sinking in. However every now and then an event really does reach out and touch you. For me this happened this morning as I read about the full extent of the bushfire hell that was unleashed in Victoria this past weekend. Kinglake, Whittlesea, these are places I know and visited many times during my five year stint as a PhD student in Melbourne. Good friends of mine live close to, but thankfully not in, the fire ravaged areas. So I want to send my sincere condolences to all the hundreds who lost their family members, homes, or livelyhoods in the devastating bushfires.
On happier news I also want to congratulate fellow blogger and co-author, Darren Naish and his wife Toni on the birth of Emma Naish.
As for myself, I'm about to head of into the field for a few days so things will be quiet on Dracovenator this week.

Another giant from the tropics: Superlucina

2009-02-08T22:37:00.000-08:00

As the blogosphere buzzes about Titanoboa I’m going to review another recent paper that hasn’t received the same degree of publicity but describes another tropical giant that is as equally interesting to me. I’m talking about Superlucina: a new generic named coined for an old species ‘Lucina’ megameris named in 1901. Superlucina megameris is a giant bivalve from the Eocene of Jamaica that was revised and interpreted by Taylor and Glover in the latest issue of Palaeontology. Yes that’s right, a paper about the proverbial Eocene clams. This one is for you Mike ;-)

That’s a big cockle. The giant bivalve Superlucina megameris. From Taylor and Glover 2009.

All joking aside, bivalve molluscs have a reputation for being simple, dull filterfeeders with little interest anyone except perhaps those few crazy taxonomists that specialize on them. Even Chris Taylor, who appears to have a boundless love for the systematic s of all biota confessed that it was hard to get excited about bivalves.
It is a tribute Taylor and Glover that they have produced such a fascinating and readable paper on these maligned creatures. However some of this credit has to go to the organisms themselves, which are fascinating once you look below their dull, clammish exterior.
Superlucina megameris belongs to the family Lucinidae which lead an unusual lifestyle. They are chemosymbiotic sulfide miners that inhabit the interface between the oxic and anoxic zones of marine sediments. By using an elongate muscular foot they build a tunnel up to the sediment surface in order to bring down oxygenated water. They also push holes down into the anoxic sediment below to bring up water with dissolved sulfides. These sulfides are oxidized by bacteria held symbiotically in the bivalve’s tissues and provide much of the nutrition that the bivalve requires.
To understand some of the unusual adaptations of S. megameris and the lucinids I first need to give a quick primer in bivalve anatomy. Bivalves are shell-bearing molluscs so that surround their body with a skirt-like fringe of tissue known as the mantle. The mantle secretes the shell, which in bivalves is divided into left and right valves that are joined dorsally along the hinge. The space between the mantle and the body forms a chamber into which the gills (called ctenidia) protrude. To ventilate the gills a water current needs to be drawn into the mantle cavity, passed over the gills and then expelled. To help with these currents many bivalves have evolved inhalant and exhalent siphons (which are modifications of the mantle. The mantle has a series of flap like, medially directed folds that partially enclose the mantle cavity. The inner fold is controlled by pallial retractor muscles which leave a long linear scar on the inner surface of the shell. This line is called the pallial line. At each end of the pallial line are two shell-closing muscles known as adductor muscles (which also leave prominent scars). Ventrally there is a muscular organ known as the foot. That will do for now.

A schematic , grossly simplified, diagram of bivalve anatomy in cross-section. Drawn hurredly by myself last night.

Ok, now to the interesting stuff. First of all lucinids house their symbiotic bacteria in the tissues of the ctenidia which makes breathing a little difficult, especially since the bacteria need to be supplied with anoxic, sulfide-rich water. In order to compensate lucinids use the anterior end of the mantle folds, as respiratory surfaces. In some large lucinids the anterior end of the inner mantle fold is thickened and pleated with complex folds that act as mantle gills. To keep the oxygenated water separate from the anoxic water, the mantle cavity is partially divided. To help with this division the anterior adductor muscle of many lucinids becomes highly elongate and extends posteroventrally, thus creating a channel between it and the mantle gills. Concomitant with this adaptation lucinids lack the posterior inhalant siphon that many bivalves have and take water in at the anterior end of the animal. In S. megameris the elongation of the anterior adductor muscle is more extreme than in other lucinid. A pustulose channel runs between the anterior adductor scar and the pallial line on internal moulds of S. megameris seems to mark the presence of a unique respiratory channel in this species that was longer than in any other lucinid.

An internal mould of S. megameris from Taylor and Glover 2009. Scars from several anatomical features impressed upon the internal surface of the shell are replicated in the mould. I have colourised these: blue – anterior adductor muscle; red – respiratory channel; yellow – pallial line; green posterior adductor muscle.

A reconstruction of the internal anatomy of S. megameris from Taylor and Glover 2009 showing the division of water inflow. Colours follow the figure above.

S. megameris also differs from other lucinids in its great size. It is the largest lucinid known and is one of the largest burrowing bivalves of all time (epifaunal bivalves like giant clams get even larger).
S. megameris inhabited a transitional zone between an open shelf region and a shallow lagoon filled with seagrass meadows. The presence of seagrass is important because it is the decaying grass that provides the sulfide that fuels the bacteria in their bodies. Although the great size of S. megameris is impressive by itself it is all the more impressive when one compares it to modern shallow water lucinids. These rarely reach a height of 10 cm (less than one third the height of S. megameris) while the vast majority range in height from 0.5 cm to 3 cm. Some chemosymbiotic bivalves inhabiting sulfide rich deep-water cold-seeps reach similar impressive sizes (as indeed did some extinct lucinids from cold seep deposits) and it has been suggested that it was the cold-seep environment that allowed for gigantism in chemosymbiotic bivalves. However the paleoenvironment of S. megameris was definitely not a deep-water cold seep. So why did S. megameris get so big? At this stage we do not know.
Lastly it is interesting to consider the relationships of Superlucina. The genus presents no particularly close similarity with any other but seems most closely related to the genera Miltha, Pseudomiltha and Eomiltha. These also tend to have the most elongate anterior adductor muscles and n some cases toothless hinge lines (like Superlucina). This potential clade was diverse in the past but is now reduced to a handful of mostly rare species, apparently being replaced by more advanced lucinids that have broader shorter anterior adductor muscles, instead using a septum to effectively divide the mantle cavity and have highly plicated mantle gills to efficiently extract oxygen. This takeover appears to have occurred rather recently, I have collected sizeable Miltha specimens from the latest Pliocene or earliest Pleistocene of southern Australia where none now live.

JOHN D. TAYLOR and EMILY A. GLOVER (2009). A GIANT LUCINID BIVALVE FROM THE EOCENE OF JAMAICA – SYSTEMATICS, LIFE HABITS AND CHEMOSYMBIOSIS (MOLLUSCA: BIVALVIA: LUCINIDAE) Palaeontology, 52 (1), 95-109 DOI: doi: 10.1111/j.1475-4983.2008.00839.x

Titanoboa and paleophidiothermometry

2009-02-06T00:44:00.000-08:00

Yes that's right a new word to describe the measuring of ancient temperatures using fossil snakes. By now most of you will have heard of the Jason Head and colleagues' paper describing Titanoboa, the largest known snake ever. For those that might not have seen it, Titanoboa was a boa that lived 58-60 million years ago in Colombia. Many fossils (mostly vertebrae) deriving from multiple individuals have been found and the largest of these came from a snake close to 13 metres in length and probably weighing in at 1.2 tons. Fossils from eight individuals were found in this size category indicating that we aren't dealing with a single freakily large individual but a species that regularly attained this gigantic size.
What I'm going to discuss however is the second part of the paper, where the authors attempt to estimate the mean annual temperature of Titanoboa's habitat by using maximum snake size. The idea rests on the observation that the size of snakes, as animals that require external sources for their body heat (ectotherms), and cannot maintain a constant internal temperature (poikilotherms), is constrained by the temperature of their environment. Makarieva and colleagues (2005a, b)observed that the largest species of many terrestrial clades of pokilotherms occur in the tropics, while the largest in the temperate realms were smaller and the largest from the polar regions were smaller still. They argued that there is a minimum mass specific metabolic rate below which an organism simply can't function. As mass specific metabolic rate decreases with increasing size there is a maximum size over which the mass-specific metabolic rate is too low. Increasing ambient temperature allows the metabolic rate to be increased and consequently a larger size can be attained.
Head et al. then used the mathematical relationship between temperature change and the change maximum attainable body size to calculate the mean annual palaeotemperature which Titanoboa experienced. Using modern green anacondas as a model for a modern snake that is probably at its maximum acheivable size (which was taken as 7.5 metres) and the temperature data for their habitat, Head et al. calculated that Titanoboa lived in a sweltering tropical forest that averaged somewhere between 31 and 32 degrees Celcius throughout the year (compare that to the 26-27 degrees averaged by modern lowland equatorial forests that anacondas live in).
It is an interesting idea but I see all sorts of problems. Firstly the size of the fossil snake may not be accurately estimated (actually this is the least likely area of inaccuracy - Head et al.'s methods seem pretty solid in this regard). My main problems are that Makariev's formula has not yet been rigorously tested (I'm not even sure HOW you would go about testing it) and most of all I don't know how we can demostrate that modern green anacondas are up against the theoretical maximal size limit for an ambient temperature of 26-27 degrees. The mere existance of exceptional individuals of anacondas and reticulated pythons reaching length close to or even slightly over 10 metres indicates that it is possible for snakes to exceed 7.5 m in the modern tropics without their metabolic rate dropping to fatally low levels. I suspect other ecological pressures (e.g. prey size, predation, availability of suitable cryptic resting places or something else entirely) may be keeping anacondas from reaching their theoretical maximum body size.

Graph from Head et al. 2009 that shows the curve of theoretical maximum size of a boiine snake against mean annual ambient temperature and the predicted temperature derived from the size of Titanoboa.

Despite all these objections, the results are remarkable in that they appear to work. That is a MAT of 32 degrees is entirely plausible, indeed expected for the tropics of the mid Paleocene Epoch. It is well known that CO2 levels were high in the Paleocene, and the world was in a greenhouse phase. During such phases there were no icecaps and we can find fossil evidence for abundant vegetation and animal life at the poles. It used to be thought that the temperature gradients between the equator and the poles were flatter than in modern times and that although the poles were nice and warm the equatorial regions were no hotter than they are now. We now know we were wrong - the tropics were fiercely hot during such times and this fits perfectly with Head's paleophidiothermometry.

REFERENCES

Jason J. Head, Jonathan I. Bloch, Alexander K. Hastings, Jason R. Bourque, Edwin A. Cadena, Fabiany A. Herrera, P. David Polly, Carlos A. Jaramillo (2009). Giant boid snake from the Palaeocene neotropics reveals hotter past equatorial temperatures Nature, 457 (7230), 715-717 DOI: 10.1038/nature07671

Makarieva, A. M., Gorshkov, V. G.&Li, B.-L. (2005)Gigantism, temperature and metabolic rate in terrestrial poikilotherms. Proc. R. Soc. Lond. B 272, 2325–2328.

Makarieva, A. M., Gorshkov, V. G. & Li, B.-L. (2005b)Temperature-associated upper limits to body size in terrestrial poikilotherms. Oikos 111, 425–436.

Finishing Fish Fortnight

2009-02-03T00:03:00.000-08:00

Ok, this is way late but you know how the real world has a habit of intruding on blogging time. Anyway this drawing is one of mine. It depicts what is perhaps the wierdest coelacanth known, Allenypterus montanus, from the Carboniferous of Montana. The bright red coloration was inspired by the resemblance between Allenypterus and the modern Pataecus fronto, a wierd ray-finned fish that is also bright red. There is a lot more I could say about this guy and its relatives - but not today.

Wierdo of the Week; Protuberum cabralensis

2009-02-02T02:16:00.000-08:00

Image from Reichel et al 2009

Imagine you found this fossil. At first glance you might think it was some kind of ornamented cranial horn but a closer look would reveal that one end bore two articulation facets on a vaguely hockey-stick shaped head. These features identify the bone as the rib of a tetrapod. But the rib of what, exactly? The row of knobs along the dorsal surface is very unusual and does not bear a close resemblance to any other known tetrapod.

These questions were raised when some of these unusual ribs were unearthed at a locality in middle Triassic sediments of southern Brazil by Father Cargnin, a preist with an interest in palaeontology. Since these ribs were isolated in an assemblage of mixed vertebrates, little could be said about their affinities. About all one could surmise is that they belonged to some exceptionally weird tetrapod. The answer came in 1989 when Father Cargnin found a partial articulated skeleton, with a skull, of the beast with the knobbed ribs at a second locality. It turned out to be a traversodontid cynodont, one of a group of plant-eating close mammal relatives that were common across the globe in the Middle and Late Triassic. Ranging in size between something that was roughly rabbit-sized up to something slightly larger but lower slung than a wolf. As advanced cynodonts they had much of the mammalian adaptive toolkit,probably including endothermy and a furry pelt, but lacked the defining dentary-squamosal jaw joint.

A reconstruction of Exaeretodon a typical traversodontid. From Wikipedia

Considering the unusual nature of the ribs, it is actually remarkable how unremarkable the rest of the animal is. The skull is much like that of any other traversodontid (there are some minor differences in skull proportions and the thickness of the skull roof).

The skull of Protuberum, above (taken from Reichel et al. 2009) in comparison to another traversodontid Massetognathus , below (taken from Romer 1967).
Anyway it has taken some time but Father Cargnin’s lumpy traversodontid has finally been published. It was given the name Protuberum cabralensis by Reichel et al. in the most recent issue of Palaeontology. The entire ribcage of Protuberum from the neck to the hips (and the dorsal edges of the hips themselves) was covered in these lumpy excrescences. The lumps are protrusions of the bone itself, not fused on dermal bones as one would expect since no cynodont is known to be armoured with dermal bones. Nonetheless these lumps would have protruded abone the level of the skin during life and were probably covered in tough, leathery or even keratinized skin. It would have made for an unusual looking animal, particularly if these lumps protruded above a layer of fur. The purpose of the knobs seems to have been defensive, perhaps against predators (they shared the earth with big crocodile relatives called rauisuchians ) or perhaps against each other.

Hat tip to Bill at Chinleana for alerting me to this publication.

References

Romer, A.S. (1967) The Chanares (Argentina) Triassic Reptil Fauna. III. Two new gomphodonts, Massetognathus pascuali and M. teruggii. Breviora 264: 1-25.

MÍRIAM REICHEL, CESAR LEANDRO SCHULTZ, MARINA BENTO SOARES (2009). A NEW TRAVERSODONTID CYNODONT (THERAPSIDA, EUCYNODONTIA) FROM THE MIDDLE TRIASSIC SANTA MARIA FORMATION OF RIO GRANDE DO SUL, BRAZIL Palaeontology, 52 (1), 229-250 DOI: 10.1111/j.1475-4983.2008.00824.x

All is well

2009-01-30T02:29:00.000-08:00

Thankyou for everyones kind support, it meant a lot to us. Anwen's operation was a complete success. The tumor was indeed attached to the underlying vein but the surgeon was able to sepparate them without any problems. The whole operation took just under an hour. After a short stay in hospital just to monitor her after the anaesthetic we took our smiling baby girl home. I'm now basking in a glow of relief and the knowledge that we made the right decision to have it removed.

This is it

2009-01-28T22:36:00.000-08:00

Anwen's big operation is today. We will be leaving for the hospital soon. Nervous? Anxious? you bet, but I keep reminding myself that a successfull operation is the most likely outcome.

Worst case of mistaken identity since Aachenosaurus!

2009-01-26T04:21:00.000-08:00

OK on with Fish fortnight,
Aachenosaurus is an infamous a case of misidentification where some pieces of petrified wood were mistaken for dinosaur bones, and a name was coined for them in the literature. The small pieces of bone in the photos above were also strikingly misidentified in the BPI catalogue as belonging to a dinosaur (though fortunately never published as such). They actually belong to a fish, a ray-finned fish (actinopterygian) to be a little more precise. As fish they are very interesting because the come from the upper Elliot Formation, and as far as I can tell are the first recognized ray-finned fish from this unit (lungfish are known from the odd small toothplate here and there). The upper Elliot Formation was deposited in arid conditions with most of the streams being small and ephemeral. Nonetheless ray-fins can’t cocoon themselves when their pond dries up the way some lungfish can and their presence indicates that some permanent water bodies, however small, existed on the upper Elliot floodplain. That’s all I can say about this fish right now - the fossil will be subjected to further prep and study.

Thankyou to everyone - and happy Australia Day!

2009-01-26T02:54:00.000-08:00

Thankyou to everyone who wished us well and has shown support. I'm sure the risks, though scary, are not very likely. Anyway I hope you all have a wonderfull Australia Day. A couple of us expats thought about singing the national anthem at the tea table this morning - but couldn't remember the words.

I'm so frightened

2009-01-22T22:23:00.000-08:00

Not for myself, for my 6 month old daughter Anwen. Forgive me this break in 'Fish Fortnight' to bring you a very personal post. I don't know why major events happen every time I try to run a theme on Dracovenator.I will throw in a bit of science so that I can keep my uber-nerd status. Plus knowing about a problem always helps me come to terms with it.
When Anwen was born she had a tiny lump in front of her fontanelle (where the frontal and two parietal bones of the infant skull fail to meet). I paid it no mind as it was virtually invisible amongst the lumpy irregualrities of a new-born's head. However it didn't straighten itself out, instead it got bigger. By this time it was obvious that it was a soft tissue structure of some sort. We showed it to the doctor who thought it was a benign cyst of some sort and that it posed no real problem because it appeared to be in front of the fontanelle. We went about getting an appointment for a general surgeon to remove it. The surgeon was a little leery of operating so close to a babies fontanelle and ordered MRI images of the lump. And what a sensible move that was. The MRI images show a tumor (probably a benign dermoid cyst)that rests largely IN the fontanelle. And therin lies the big problem.
But first a little about dermoid cysts and why they are classically located on the midline of a person.
It all comes down to early development of the embryo. Anwen, like all chordates, has a dorsal nerve chord formed by a process called neurulation. In neurulation a stripe of cells from the outer layer (the ectoderm), that runs down the back of the embryo, thickens, curls over and eventually pinches off to form a tube. This tub is what becomes the brain and spinal chord. You can see the process nicely in this diagram (of an amphibian - but the process is more or less the same in humans) which I nicked from Pharyngula. Incidentally Pharyngula has a much more detailed post about neurulation if you want to know more.

What happened in Anwen's case is that a few cells thay were supposed to stay in the ectodermal layer above the neural tube and go on to form the skin (the white tissue in the diagram above) became trapped under the ectodermis when the neural tube closed over. Thus stuck out of place but already set on the path to skin-hood they grow into a little sac of skin-like cells that we call a dermoid cyst. Normally these present no problem at all and can be removed with the minimum of fuss. However in Anwen's case the position is a real bummer. The cyst is not surrounded by fatty tissue as they often are and as a result the lower surface is in contact with the structure underneath. This just happens to be the sagittal sinus. This sinus is a space bounded by the dural membranes that runs between the hemispheres of the brain and collects the venous blood and returns it back to the heart. Several veins that drain the brain enter into the sinus in the vicinity of Anwen's cyst (or at least if I understand the surgeon correctly). These veins are not robust structures like the ones you find in your limbs, they are delicate membranous structures that are easily torn. Such a tear can have catastrophic even fatal consequences.
So there you have it. Anwen has a tumor on her head that if left will grow larger, impede skull development and probably eventually constrict venous bloodflow from the brain. To remove it is a tricky operation with the risk of tearing a dural vein which may lead to her death. We have the services of a skilled neurosurgeon of high repute but we are still understandably frightened. Its not an easy decision for a parent to expose their child to risk, even if small and for her greater benefit in the long run. Nonetheless the operation must go ahead and will probably happen next week. I'll let you know how it goes.

Anwen and her pesky little bump

Misleading Mitochondria and Ancient Neopterygian Fossils

2009-01-21T01:23:00.000-08:00

Last post we looked at the basics of ray-finned fish classification and some of the problems associated with them. Foremost among these are two rather dramatically different topologies. Morphology supports a clade called the Neopterygii which includes ginglymods, halecomorphs and teleosts whereas mitochondrial genetics support an ‘Ancient Fish Clade (AFC)’ that groups chondrosteans, ginglymods and halecomorphs to the exclusion of teleosts. Divergence dates based on the molecular clock are also dramatically older than minimal dates based on the fossil record. Hurley et al. (2007) tackle both problems with a two-pronged approach. Firstly they relook at the early ray-finned fossil record, scrutinizing it for the first appearance of derived characters diagnostic of these major groups and incorporating the data into a new cladistic analysis. Secondly they assembled a new, comprehensive molecular data set of four nuclear genes 29 species covering all the relevant clades (except the cladistians), thus is the first analysis capable of addressing the timing of the whole genome duplication event.
The tree based on the morphological data found strong support for the Neopterygii and virtually no support for the ‘Ancient Fish Clade’ at all. Indeed when the AFC topology was enforced upon an analysis that included only the living taxa the tree length grew by 80 steps (125% of the number of steps in the shortest possible tree) and found just one character that could be interpreted as a synapomorphy of this clade. Clearly the morphology doesn’t just fail to support the molecular ‘AFC’ it is strongly contradicting it. Analysis of the nuclear gene data also strongly supports the neopterygian clade over the AFC. Thus the signal for the AFC is coming from the mitochondrial genes alone. Given that this data set is so at odds with morphology, nuclear genes and the fossil record it seems likely that the source of error is the mitochondrial data. Perhaps more interesting is the morphological analysis that includes the fossils. Neopterygii continues to be strongly supported but the divergence date estimates have changed. Two fossils in particular were found to be significant: Brachydegma and Discoserra. Brachydegma from the Early Permian (285 million years) of Texas was previously regarded as a basal actinopterygian that diverged before the chondrostean-neopterygian split. However Hurley et al. found that it had a number of characteristics of Halecomorpha (that is the bowfin and its fossil relatives), such as an enlarged gular plate, a medial shelf at the front end of the maxilla, and possibly a posteriorly indented maxilla. The latter character is less secure because it depends on the interpretation of a small elliptical patch of differing ornament on the rear edge of the maxilla. If this patch is interpreted as a fused-on scale, then the maxilla does have the classic halecomorph indented maxilla (see figure below).

Brachydegma (from Hurley et al. 2007) on the left and the modern bowfin (Amia) on the right (not to scale; from Grande and Bemis 1998). Two diagnostic features of the Halecomorphi are colourised – the posteriorly indented maxilla (red) and the very large gular plate (green).

Sure enough Brachydegma comes out as the basal most member of the Halecomorphi in their analysis. As an halecomorph, Brachydegma is part of the neopterygian crown-group and pushes the origin of this clade back the Palaeozoic Era, before the big extinction event at the end of the Permian Period. The previous oldest known crown-group neopterygians were the parasemionotids (also halecomorphs) from the Early Triassic of Madagascar and Greenland. Discoserra from the Early Carboniferous (320 million years) of Montana (the famous Bear Gulch Limestone fish deposits) is a far older fish, and is not apparently a member of the neopterygian crown group but it has many of the synapomorphies of the crown-group indicating that by this early stage the neopterygian bodyplan was mostly in place. Previously Discoserra was thought to be an early cladistian.

Discoserra, from Lund 2000.

The new fossil data places the origination of the neopterygian crown group into the Paleozoic Era, long before the big Permo-Triassic mass extinction event of 251 million years, and at least 40 million years earlier than the previous oldest crown-group neopterygian and somewhat closing the gap between the molecular and palaeontological dating of the Neopterygian crown-group origination. Furthermore molecular clock dating using the nuclear gene data, rather than the mitochondrial genes yields a more recent range of dates 271-371 million years that actually ecompasses the age of Brachydegma, thus the discrepancy is more or less resolved. Once again it appears that the mitochondrial genes are giving misleading results, but why this is so is not immediately clear. No particularly ancient crown-group teleosts were recognized in this study so the fossil based minimum age for this clade is unchanged. However the new nuclear genetic data were used to estimate the divergence of the crown group. Like the estimates for the age of the neopterygian crown-group the estimates for the teleost crown-group based on nuclear genes are considerably younger than the estimates based on mitochondrial data. Thus using these new age estimates the discrepancy between molecular and palaeontological dates closes to a minimum of 30 million years.
Lastly Hurley et al. look at the timing of the whole genome duplication and how it relates to the explosive radiation of teleost fishes. The duplication event is indeed shown to be a feature of the teleost stem, as its products appear to be present in all living teleosts but are not found in the other surviving actinopterygian groups. This suggests that the duplication event most likely happened sometime in the Permian or Triassic, with the most recent possible occurrence being the Mid Jurassic, before the first appearance of crown-group teleosts in the fossil record. However the explosion in teleost diversity does not get underway until the Late Cretaceous, demonstrating a considerable lag between the duplication event and the rapid diversification event. This falsifies the hypothesis that the duplication was the direct causative agent of diversification.
In conclusion, this is a case where the morphological signal appears to have given a more reliable estimate of phylogeny than mitochondrial genes, whereas the huge discrepancy in divergence date estimates were a product of both overlooked fossil data and misleading signal based on the same unreliable genetic data.

Grande, L. and Bemis, W.E. (1998) A comprehensive phylogenetic study of amiid fishes (Amiidae) based on comparative skeletal anatomy. An empirical search for interconnected patterns of natural history. Society of Vertebrate Paleontology Memoir 4: 1-690.

Hurley, I.A., Lockridge Mueller, R, Dunn, K.A.,Schmidt, Friedman, M., Ho1, R.K., Prince, V.E., Yang, Z., Thomas, M.G. and Coates, M.I. (2007)A new timescale for ray finned fish evolution. Proc. R. Soc. B 274, 489–498

Lund, R. (2000) The new actinopterygian order Guildayichthyiformes from the Lower Carboniferous of Montana (USA). Geodiversitas 22, 171-206.

Problems in Ray-Finned Evolution.

2009-01-18T23:22:00.000-08:00

I’ve touched on the tension between genetic and morphologic data in this post and the comments it attracted. As I stated then both sets of data are the products of a single history and should therefore be more or less in accord. When they are not, well then it is our job as scientists to find out why. Gone are the days of simply giving a hurumph and declaring one’s personally preferred set of data to be correct and the other erroneous. I want to feature a 2007 paper by Hurley et al. as an excellent model for the unification of both sources of data. Although a few years old now, it remains one of my favourite bits of palaeontological research. And it doesn’t even feature dinosaurs. No, it is about the phylogeny of ray-finned fish. But before I can get to the paper in question I will need to bring my readers up to speed with the relevant issues in this post before turning my attention to the paper itself in my next post.
For those not aquainted with fish taxonomy, I’ll first give a quick rundown of the groups involved. All vertebrates that replace their cartilaginous inner skeletons (endoskeleton) with bone are known as Osteichthyes (literally “bony fish”). Note that not all fish with bone are osteichthyans. Several extinct groups like placoderms and osteostracans covered their bodies in large plates of bone. However this bone is derived from skin (ectodermal) tissue and remains superficial to the endoskeleton which remains cartilaginous. Also note that we tetrapods also replace our endoskeletons with bone: we are bony fish (albeit highly terrestrially adapted bony fish). Anyway the bony fish clade divides into two great clades: Sarcopterygii (including tetrapods) and Actinopterygii. It is the Actinopterygii, or ray-finned fish that concern us here. Actinopterygians are a clade and can be diagnosed by a bunch of characteristics, the most obvious one being that there is just one dorsal fin. Of course the path of evolution is rarely simple and we find that many modern actinopterygians divide their single dorsal fin into an anterior spiny portion and a posterior portion with soft rays. Sometimes the dorsal fin is bilobed with a dip in the profile between the spiny and soft sections but more often there is a finless gap, thus two dorsal fins are secondarily acquired.
The evolutionary success of ray finned fish cannot be overstated. In terms of diversity they outnumber all other vertebrate clades put together 2:1 and exhibit a jaw-dropping array of specializations, some of them nightmarishly bizarre to our eyes. Living ray-fins can be divided into five clades, the vast majority of ray-fins belong to just one of these the Teleostei. The other four groups are the cladistians (bichirs), chondrosteans (sturgeons and paddlefish, not to be confused with the chondrichthyans which are the sharks, rays and ratfish), ginglymods (gars*) and halecomorphs (bowfin).

Polypterus, the bichir, a living cladistian from Central Africa. Image from wildwoods.co.uk

Pallid sturgeon, a chondrostean. Image from wikipedia.

Lepisosteus, gar, a living ginglymod from North America. Image from wikipedia.

Amia calva, the bowfin. The sole surviving halecomorph. From North America. Image from wikipedia.

The staggering diversity of modern ray-fins is actually a relatively recent phenomenon compared to the venerable age of the total actinopterygian group. The first ray-fins appeared no later than the Late Silurian, when we find the first fossils of their sister group, the Sarcopterygii (e.g. Psarolepis in China) whereas the steep rise in diversity and disparity didn’t really start until the Late Cretaceous and is restricted to the teleost clade. One intriguing feature of living teleosts is that their entire genome has been duplicated. Some have suggested that this duplication event may have been the impetus for the teleost diversification. With two copies of every gene it is easy to imagine that duplicates of essential genes that have little freedom to vary without compromising the organism would be free to vary, perhaps allowing a more rapid exploration of morphospace.
It is universally agreed on both morphological and molecular data that the cladistians are basal to all other rayfins, but the relationships of the other clades remain contentious. Morphological analyses support a ladder like arrangement with chondrosteans, ginglymods and halecomorphs forming serially closer outgroups to the teleosts. The clade including ginglymods, halecomorphs and teleosts is known as the Neopterygii and is characterized by, amongst other features, loss of the clavicle bone, a vertical hyomandibula (jaw suspensorium) and a mobile maxilla (but not in modern ginglymods). Molecular data based on sequences of mitochondrial genes however gathers these three groups into an ‘ancient fish clade’ that is the sister group of teleosts. The following diagram from Hurley et al. (2007) illustrates these two different arrangements well.

The shape of the tree is not the only source of molecular vs. morphological tension in ray finned fish evolution. Estimates of the timing of the divergences between these clades is also dramatically different when using the different data sources. For example the oldest crown-group teleost (reminder: the crown-group is the group descended from the most recent common ancestor of all extant species) in the fossil record dates from the Late Jurassic (151 million years), whereas mitochondrial data estimates the divergence date at either the Early Permian (285 million years) or Early Carboniferous (334 million years) depending on the method used. That’s a difference of 134 to 183 million years. Now we can always expect that a clade will not show up immediately after its divergence from its sister group, due to low diversity and low abundance but this difference is extraordinary. Other molecular divergence dates are also strongly discordant with the fossil data, for instance the bowfin-teleost split (which would provide a minimum age of crown-group Neopterygii) is estimated to range from 417-390 million years (Late Silurian to Mid Devonian) using mitochondrial data whereas the palaeontological date of neopterygian crown-group is 245 million years (Early Triassic). However the picture isn't quite as bad as it once seemed and we shall look at how improvements in our understanding of both sets of data is straightening out this problem in the next post.

*Note to Australian fisherpeople, the ‘garfish’ you will be familiar with are part of the vast teleost radiation and are not ginglymods of any sort.

Hurley, I.A., Lockridge Mueller, R, Dunn, K.A.,Schmidt, Friedman, M., Ho1, R.K., Prince, V.E., Yang, Z., Thomas, M.G. and Coates, M.I. (2007)A new timescale for ray finned fish evolution. Proc. R. Soc. B 274, 489–498

Where do spiny sharks go?

2009-01-15T01:29:00.000-08:00

Hi and welcome to fish fortnight on Dracovenator. You may notice a slight change in style here, as a new year's resolution I'm going to try to write for a more general audience. Does this mean I'm dumbing Dracovenator down? No, I'm just going to try to stop assuming a lot of specialist knowledge on a part of my readers, and will throw in some more basic anatomy for the Form and Function students I'll be teaching later this year.
Anyway by pure coincidence a bunch of fish-related items have come up all at once so I'm running a kind of fish-festival over the course of the next two weeks.
The first of these is a new paper in Nature this week by Martin Brazeau, which desribes the braincase and jaws of an acanthodian (popularly called spiny sharks, although they are not sharks, at least not in the conventional sense). Why is this a big deal? I'll get to that, but first some background.
Most modern vertebrate animals have jaws (only lampreys and hagfish do not). Those that have jaws belong to the great clade Gnathostomata (literally 'jaw-mouths'). Modern gnathostomes can be further divided into two clades: The cartilaginous fish (Chondrichthyes) including sharks and rays and the bony vertebrates (Osteichthyes)including everything else from goldfish to humans.
Both groups are monophyletic, that is they include all descendants from a common ancestor, thus neither group was ancestral to the other, both having split from a common jawed ancestor somewhere back in the past (probably in the Late Ordovician or Early Silurian Period).
Now there are some fossil jawed vertebrates that don't fit into either of these two clades. These are traditionally placed into two groups: The placoderms (armoured fish) and the acanthodians (so-called spiny sharks).

Dunkleosteus, a giant placoderm. Painting by Charles R. Knight. From universe-review.ca

How do these groups relate to the surviving Chondrichthyes and Osteichthyes, or in other words, what is the shape of the first part of the evolutionary tree of jawed vertebrates?
That has been a big mystery indeed. Just about every possible arrangement has been suggested. Placoderms are either regarded as the sister group of all other gnathostomes (that is they branched off first and the others all share a more recent common ancestor) or are thought to share a closer relationship with Chondrichthyes than with Osteichthyes. Nevertheless the plates of dermal bone which encase the front end of these fish has been thought to be an evolutionary novelty (synapomorphy in technical parlance) which marks out the placoderms as a monophyletic group.
The acanthodians have proven even more difficult to place, partly because the internal skeletal anatomy of most species has not been preserved (because like hagfish, lampreys and sharks it was cartilaginous). The favoured hypothesis of more recent years was that acanthodians shared a close relationship with Osteichthyes, that is they split from the line leading to bony vertebrates after the placoderms and chondrichthyans had already split and started their own evolutionary journeys. This was the position taken by Phillippe Janvier in his book 'Early Vertebrates' (1996, Oxford University Press)- an excellent book by the way. Once again the group had been thought to form a clade largely on the characteristic of bony spines supporting the leading edge of their paired fins and some details of their scales. Recent discoveries have shown that both of these features are probably general features for early gnathostomes that were lost in the modern groups, rather than evolutionary novelties unique to acanthodians. It should be noted that even back in 1996, Janvier noted that acanthodian monophyly wasn't all that strong and presented the suggestion that some acanthodians might turn out to be more closely related to chondricthyans (what we would call stem group chondrichthyans) while others might be stem group osteichthyans.

A diversity of acanthodians by Stanton Fink. Image from wikipedia-commons.

Enter Brazeau's recent paper. It includes a cladistic analysis of early jawed vertebrate phylogeny (the branching pattern of evolution) that uses individual genera, rather than large monophyletic groups. Lo and Behold, Janvier was right, or at least on the right track. Indeed Brazeau's analysis finds former acanthodians falling out all over the tree. Some are stem-group gnathostomes that branched away before modern gnathostomes split into Chondrichthyes and Osteichthyes, others are stem-group chondrichthyans others are stem-group osteichthyans. In particular the former acanthodian that forms the centrepiece of the paper, Ptomacanthus, is found in some of his trees to be the closest sister group to the gnathostome crown-group (the crown-group is the clade including the extant species and all descendants of their most recent common ancestor - in this case the common ancestor of Chondrichthyes and Osteichthyes). Ptomacanthus is special because unlike most other acanthodians, including all the early, more relevant species, does preserve some of its internal skeleton, namely the braincase and the jaws. The braincase is remarkably primitive, actually looking more like that of a placoderm than a crown-group gnathostome. This unusual combination of characters (externally crown-group like but internally more primitive) helps to break up the acanthodian group and gives this new tree. There are other odd things in this tree, for instance placoderms are not found to be monophyletic either but that is a topic for a later post (and further investigation methinks).

UPDATE: Check out the ever-informative Catalogue of Organisms for a post that slipped past me before for a little bit more about acanthodians.

Martin D. Brazeau (2009). The braincase and jaws of a Devonian ‘acanthodian’ and modern gnathostome origins Nature, 457 (7227), 305-308 DOI: 10.1038/nature07436

A new Beipiaosaurus - beautifull plumage!

2009-01-12T23:26:00.000-08:00

We're just under a fortnight into the new year and already the new dino papers are stacking up. The DML brings news of Ceratonykus a newly named alvarezsaur. And PNAS have published a short paper on a stunning new specimen of the therizinosaur Beipiaosaurus. This specimen is much less badly fragmented, than the holotype but sadly still only consists of the front end of the skeleton. It gives us all sorts of new details to mull over. First and foremost are the weird large single filament feathers that line the neck, back and tail (present in the holotype but not the new specimen). This fossil combined with last year's Epidexipteryx is showing us that a diversity of feather forms, now extinct, evolved before the pennaceous feathers that dominate modern birds plumage. In this case the feathers take the form of stiff, single filaments, that are about 2mm in diameter. The authors call them EBFFs (Elongate Broad Filamentous Feathers) but I will simply call them 'quills' and I really wonder whether they had some spiny defensive function. The apparent lack of any modern style pennaceous feather, with a central rachis and rows of barbs on either side, does suggest that therizinosaurs are not so closely related to oviraptorosaurs (which have pennaceous feathers in spades) as once thought. This does back up recent analyses based on skeletal anatomy which have not been returning an oviraptorosaur-therizinosaur clade of late. Furthermore these quills bear more than a pasing resemblance to the structures of the tail of the ceratopsian Psittacosaurus. The authors suggest what I guess a great number of us have wondered: did feathers evolve much earlier in archosaur history than we currently recognise?
Of course the complete skull alone is reason enough to make theropodophiles drool. Intriguingly it appears quite derived (it acyually looks like a little Iguanodon, oops that should be Dollodon skull) which indicates that cranial modification occured earlier than some of the postcranial modifications that therizinosaurs are famous for, e.g. the re-enlarged hallux, or big toe.
Other cool details include the outlines of a throat pouch, a feature that seems to have been reasonably widespread amongst dinosaurs.
2009 is shaping up to be a good year!

X. Xu, X. Zheng, H. You (2009). A new feather type in a nonavian theropod and the early evolution of feathers Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0810055106

The littlest sauropodomorph?

2009-01-04T23:14:00.001-08:00

The known remains of Thecodontosaurus minor, the scale bar was added by me but the rest is taken directly from Haughton 1924

What better way to kick off the new year but with a post about basal sauropodomorphs from South Africa?
In 1918 Sidney Haughton named a small collection of tiny sauropodomorph bones from the Elliot Formation, near the town of Maclear, Eastern Cape, as Thecodontosaurus minor. There isn’t much to the specimen, just a cervical vertebra, a tibia and a fragmentary ischium. This little guy has remained in almost complete obscurity ever since it was named. All recent treatments that even give it a mention regard it as either a nomen dubium, or as a synonym of Massospondylus carinatus. However there are some odd things about these remains that suggest this taxon deserves a closer look. Firstly it is very small, with the tibia just over 10 cm, a length not much greater than that of Microraptor zhaoianus which is widely cited as the smallest non-avian dinosaur. Usually T. minor is dismissed as a juvenile but this is not necessarily the case because it appears that the neurocentral suture of the cervical vertebra is closed. I freely admit that I’ve only ever given the specimen a cursory look, and that this needs to be checked more closely. If it is closed then it would indicate the individual was approaching maturity. One does have to be careful when using the closure of neurocentral sutures to age a dinosaur but in this case there is abundant evidence that basal sauropodomorphs did not close their neurocentral sutures until close to maturity, or even after adult size had been reached. Indeed the majority of all presacral vertebrae preserved in the basal sauropodomorph record have separated along their neurocentral sutures. Now if T. minor really is a mature, or near mature individual, then it would have the smallest known adult size of any sauropodomorph. Just for fun here is the silhouette of a small sauropodomorph scaled to a tibia length of 10 cm, next to the hand of Brachiosaurus brancai.

So what else is odd about this taxon? Well the ischium is a little odd. Although incomplete there is a short stretch of the ischial shaft preserved behind the proximal obturator region. This shaft is unusually flattened, whereas most basal sauropodomorphs, have an ischial shaft that has equilaterally triangular cross-section. Amongst basal sauropodomorphs I’ve only seen this type of flattened ischial shaft in Thecodontosaurus, Anchisaurus and Mussaurus. By itself this isn’t enough to hang a taxon on but it is enough to reject synonymy with Massospondylus (unless of course there is postmortem crushing at play, or I've misjudged the amount of ischial shaft that is present).
However there is one other aspect of this little fossil that has me kicking myself for not looking more closely at it when I had the chance. It would appear that this little fossil comes from the lower Elliot Formation. This became apparent after I read the original (unillustrated) description, rather than Haughton’s later 1924 illustrated monograph on the fossils of the Stormberg group. Quoting the 1918 paper the horizon in which this specimen was discovered was the “Red beds, just below halfway from base”. As I’ve mentioned before on this blog ‘red beds’ is the old name for the Elliot Formation and this Formation comes has two members, of different age, depositional style and fauna. At the southern end of the outcrop area (where Maclear is located) the lower Elliot makes up about two thirds of the stratigraphic thickness of the Elliot Formation, placing T. minor in the lower Elliot and puts paid to any notion that the specimen is a juvenile Massospondylus. This is remarkable for the sauropodomorph fauna of the lower Elliot consists entirely of large robust forms. Indeed small vertebrate fossils of any sort are exceedingly rare. Indeed there are only two named taxa that would have massed less than 50 kg as adults: the ornithischian Eocursor and the trithelodontid cynodont, Elliotherium, both of which are based on unique specimens. A minute sauropodomorph from the Triassic of South Africa would be an interesting and welcome addition.
So is T. minor a valid taxon? That is a difficult question. The known remains do not present any obvious autapomorphies other than its tiny size. If it can be confirmed either by histological sampling of the tibia, or micro ct scanning of the cervical vertebrae, that these are indeed the remains of a mature individual then, yes I think it would be a valid taxon, though just barely (on the basis that it can be excluded from all other known Triassic sauropodomorphs on the basis of size and the mix of characters it displays). Sadly the known remains are utterly inadequate for narrowing down its phylogenetic placement among basal sauropodomorphs, it could easily fall anywhere between Thecodontosaurus and Melanorosaurus. So there is little justification for keeping it in Thecodontosaurus, a new name will have to be coined for it but I think that that action would be best held off until such time as better remains come to light. I just hope that I might find some on my next field excursion.

References

Haughton, SH (1918) On a new dinosaur from the Stormberg beds of South Africa. Ann. Mag. nat. Hist. 2: 468-469.

Haughton, SH (1924) The fauna and stratigraphy of the Stormberg series. Ann. S. Afr. Mus. 12: 323-497.

HAPPY NEW YEAR and I'll be Back real soon

2009-01-02T04:22:00.001-08:00

Hi guys,

You've probably twigged that I don't have an internet connection at home, so I'm limited to posting when I'm at university. I've been enjoying a long break over the christmas - new year season, hence the long silence.
I'm just going to show a interesting little curio that crossed my desk late last year. A gem and mineral dealer bought it in thinking he'd got hold of a dinosaur skull. At the time the specimen was embedded in what looked like sandstone matrix, but it was clear that it did contain some vertebral material and wondered if it was a short section of articulated vertebrae. While I made it clear that I wouldn't publish on fossil material of dubious origins and support the market in vertebrate fossil material, Celeste offerred her skills as a preparator to clean it up for him (hey we've got a family to support!). As the 'sandstone' came off it became clear that this was a fake - not even a very good one. Lumps of real dinosaur bone had been cobbled together with glue, resin and plaster. The biggest bit is a vertebral centrum, probably belonging to a sauropod based on its camellate internal structure. Nonetheless the piece does have its charm, it was only after preparation that I saw the 'skull' that the forger was trying to make. It kind of looks like a pig-snouted crocodile.

More temnospondyls: old big eyes from the Moenkopi

2008-12-23T01:34:00.000-08:00

Temnospondyls are among the several groups I’ve dabbled in, and they certainly deserve more attention than they get. They are the most speciose and long-ranging of the ancient tetrapod groups. I don’t intend to open the can of worms surrounding what exactly a ‘tetrapod’ is – I’ll just use it in the Clackian sense (sarcopterygians with limbs and digits or descended from ancestors that had limbs and digits). We don’t even know whether or not temnospondyls are stem amphibians, although I wouldsay that the case is looking very good right now. In anycase my interests lie with temnospondyls that lived in the Triassic, after the main clades of modern amphibians had already diverged. One of these groups are the enigmatic brachyopids.

Batrachosuchus, a classic brachyopid from the Early Triassic of South Africa.

Brachyopids present a classic case of the difficulty in disentangling convergence from relationship in an extinct group. Their shortened parabolic skulls bear more than a passing resemblance to another group of temnospondyls, the dvinosaurs (dinosaurs are good but a dvinosaur is devine – sorry, couldn’t resist) and indeed the consensus opinion is that brachyopids are the derived descendants of earlier dvinosaurs.

Dvinosaurus, a dvinosaur from the Late Permian of Russia.

However brachyopids share some unusual derived characters with other derived temnospondyls from the Triassic known as stereospondyls. Some of these characters include: a double occipital condyle; the pterygoid bone in the palate forms a long broad suture with braincase rather than a narrow synovial contact; and lack of exposure of the opisthotic in the occiput. I took this to mean that brachyopids really were stereospondyls and share a more recent common ancestor with long snouted stereospondyls like Paracyclotosaurus than they do with short snouted dvinosaurs like Dvinosaurus , or rather that is what I found in my cladistic analysis that I performed for my PhD thesis, later published with my supervisor, Dr Anne Warren. This kind of ecophenotypic convergence seems to have happened multiple times in the evolution of crocodile snout shape (though maybe a little less than previously thought if false gavials and gavials really are sister taxa) and seeing it in temnospondyls was almost to be expected. Of course the situation isn’t quite so simple, for instance some late surviving incontrovertible dvinosaurs DO develop some of the stereospondyl synapomorphies convergently (even more disconcerting is that they develop them at the same time that the streospondyl lineage does!). So it really maybe the case that it is the unusual and apparently unrelated features of stereospondyls that are the convergences while the broad trophic adaptations such as snout shape are a true indication of relationship. It’s a wonderfull and truly juicy puzzle that I once wanted to tackle myself, but I’m so thoroughly bogged down in dinosaur projects now that I can’t see myself getting to it anytime soon. Furthermore the travel involved in unraveling this tangle is pretty daunting. Significant fossils are scattered all over the globe, with important specimens in many parts of the US, England, Argentina, South Africa, Australia and Russia. So for now I am happy to sit back and watch the progress from the sidelines. One researcher who has really picked up where I left off is Marcello Ruta. Marcello hasn’t solved the problem yet but he has started really squeezing more phylogenetic information out of temnospondyl fossils than I ever did.
One little step on the road to understanding brachyopids has just been published by Marcello together with John Bolt of the Field Museum. They looked at Hadrokkosaurus bradyi a large brachyopid from the Moenkopi Formation of the US and one of the better known brachyopid names. The name Hadrokkosaurus means ‘big eyed lizard’ and the skull disseminated around the world in the form of casts truly does have big goggling orbits.

The famous skull, referred to Hadrokkosaurus.

It comes as a surprise to many, myself included, that this famous skull isn’t the holotype. Indeed the holotype doesn’t even preserve orbits at all,for it is an isolated lower jaw ramus. Furthermore this lower jaw was found over 100km away from the skull. With a name like Hadrokkosaurus it is hard to dispute that the Welles had the skull in mind when he erected the name. However the jaw was found first and originally named Taphrognathus, which was unfortunately preoccupied by a conodont (NOT an arthropod for once!). Thus Hadrokkosaurus was created to replace Taphrognathus, leaving the lower jaw as the holotype specimen. This is a pity and it has created a messy taxonomic situation. Jupp and Warren suggested way back in 1986 that the lower jaw might not belong to the skull, and might not even be a temnospondyl at all! They cited the presence of an external mandibular fenestra, teeth that are partially sunk into sockets, weak surface ornamentation, a splenial bone that does not participate in the symphysis of the jaw and a surangular-prearticular contact behind the jaw joint, to suggest that the jaw is infact an archosaur (archosauriform in recent classifications). I need not remind you that a pair of roundned lower jaws fitting onto something roughly the size and shape of a dustbin lid makes for a pretty unusual archosauriform, particularly one of proterosuchian grade with subthecodont teeth. Because of the uncertainty surrounding the identity of the type jaw Anne Warren and Caudia Marsicano decided to bestow a new name upon the well-known skull, they called it Vigilius wellesi. The genus name means 'watchfull' or 'vigilant' and sort of echoes the original 'big eyed lizard'. The species name obviously honours Samuel Welles, the original describer of Hadrokkosaurus.
So is Hadrokkosaurus a weird-ass archosauriform? Definately not: Ruta and Bolt demolish any chance that these jaws belong to an archosauriform. The jaw shows some additional primitive bones (three coronoid bones, and two splenial bones) that are not found in any crown group amniotes, let alone in archosauriforms.
So its not an archosauriform what is it? Well it is without doubt a brachyopid after all. The so called un-temnospondyl like features are either artefacts of damage or misinterpretation (e.g. the so-called external mandibular fenestra) or are derived characteristics that are present in other temnospondyls (e.g. reduced ornamentation of the bone surface, subthecodont teeth and failure of the splenial to reach the symphysis). Furthermore a number of other characteristics, most obviously the honking big retroarticular process, are fairly convincing synapomorphies of Brachyopidae.
So are Vigilius and Hadrokkosaurus the same thing after all? I think they probably are, although Ruta and Bolt suggest that they may be two different brachypoids on the basis of non-matching jaw curvature. However we are dealing with different individuals of different sizes in a taxon that did not have precise occlusion in anycaseso slight differences in jaw curvature not convince me that they are distinct. Indeed both the lower and upper jaws seem to me to have slightly squared-off tips and angular margins that differ ever so slightly from the typical parabolic jawlines of most other brachyopids. This observation coupled with the highly reduced ornamentation of both Vigilius and Hadrokkosaurus (extreme even for brachyopids) and their occurence in the same formation leads me to suspect that the two taxa are indeed the same. We'll just have to wait to find a skull with jaws included to prove it.

The skull of Vigilius (left) and the jaws of Hadrokkosaurus (with the right side mirrored) on the right. Taken from Ruta and Bolt (2008).

Apart from clearing up the identity of Hadrokkosaurus, Ruta and Bolt's paper is important because it demonstrates that a great deal of phylogenetic information can be gleaned from the lower jaws. They analyse lower jaw characters alone and recover a topology that has much in common with my own (there is some weirdness but what do you expect from analysing just one organ system?). In contrast my analysis included a paltry 14 lower jaw characters and probably would only be able to resolve a couple of nodes, if any at all, if run by themselves. Thats a whole lot of information that shouldn't be ignored.

references

Jupp R, Warren AA (1986) The mandibles of the Triassic temno−
spondyl amphibians. Alcheringa 10: 99–124.

Ruta M, Bolt JR (2008)The brachyopoid Hadrokkosaurus bradyi from the early Middle Triassic of Arizona, and a phylogenetic analysis of lower jaw characters in temnospondyl amphibians. Acta Paleontologia Polonica 53: 579-592

Warren AA, Marsicano C (2000) A phylogeny of the Brachyopoidea
(Temnospondyli, Stereospondyli). Journal of Vertebrate Paleontology
20: 462–483.

Yates AM, Warren AA (2000) The phylogeny of the “higher”
temnospondyls (Vertebrata: Choanata) and its implications for the
monophyly and origins of the Stereospondyli. Zooogical Journal of the
Linnean Society 128: 77–121.

Predictions for 2009

2008-12-19T05:34:00.000-08:00

I enjoy reading John Hawks' blog for a change of pace away from matters archosaurian. I quite enjoy reading his predictions and seeing how they pan out. So I'm giving it a go here. These are my predictions for the big stories in dinosaurs and dino-related science in 2009. (Some obvious ones are ommited because I have insider knowledge and that would be cheating).
Arranged from most likely to most far out.

1) A new genus in the Tyrannosauridae will be named. There are several contenders floating around, lets hope they will see the light of publication next year.

2) An Early Jurassic tetanuran will be found (several have been claimed but none stand up to scrutiny).

3) The first incontrovertible evidence (e.g. a neck column)for a mamenchisaur outside of Asia.

4) A definitive non-avian dinosaur parasite will be found (probably will be a louse or a mite amongst the feathers or protofeathers of something from Liaoning).

5)A major descriptive monograph from the Sereno stable. Hopefully Eoraptor or Jobaria.

6) A complete well-preserved non-dinosaurian dinosauromorph skull will be found.

7) A Late Norian-Rhaetian herrerasaur will be announced.

8)An incontrovertible proto-pterosaur will be announced (I know there are some supposed contenders but I don't think they qualify as 'incontrovertible').

9) Good evidence that air sac systems are basal to crown group archosaurs will be published.

10) A site spanning the Late Pliensbachian to Aalenian will be found with evidence for a mass extinction.

Feel free to suggest your own or let me know if one or more of these is indeed a reality in the pipeline!

Picture of the Day: a Temnospondyl

2008-12-17T23:33:00.000-08:00

This is a drawing I did for a book that never appeared. A pity, since I don't even have the original, just this bromide. It is one of my better works and portrays the Australian Middle Triassic Paracyclotosaurus davidi, a member of the Mastodonsauridae (but thats another story).

Dracovenator by request: the age of the Elliot

2008-12-14T23:35:00.000-08:00

Randy and Bill asked an apparently simple question that will require an involved answer. What age is the Elliot Formation? What follows is a detailed account of my thoughts that will probably get to technical for those without a geological bent.
Still here? Great I’ll try to make it worth your while. As I mentioned in the last post the Elliot Formation occurs near the top of the vast sedimentary pile that fills the famous Karoo Basin of South Africa. It underlies the Clarens Formation and overlies the Molteno Formation. Dating the formation is difficult as there is little to constrain it, there are no known ash or lava beds within it that have been radiometrically dated, and the formation lacks any marine microfossils or palynomorphs (spores and pollen) that could be used to date it. The upper constraint on its age comes from the Drakensburg lavas that overlie the Clarens Formation. These represent a rapid pulse of volcanism that is precisely dated to 183 million years ago, which places it at the Pliensbachian-Toarcian boundary of the Early Jurassic in the timescale of Gradstein et al. (2004). Thus the Elliot Formation cannot be any younger the Toarcian-Pliensbachian boundary. At the other end, the constraint on the maximum age of the Elliot Formation is much woollier. The Molteno Formation is said to have palynomorphs of Carnian age, but this is a thick unit and it is not known how much younger the upper parts of the Molteno Formation gets. Furthermore it is now know that terrestrial ‘Carnian’ deposits (e.g. the famous Ischigualasto Formation of South America) actually correlate with the latest Carnian to early Norian stages of the marine sequence. A Carnian/Norian age for the Molteno Formation is also supported by the vertebrate fauna of the Pebbly Arkose Formation of Zimbabwe which is presumed to be a lateral equivalent of the Molteno Formation. This fauna consists of a rhynchosaur and a primitive dinosaur that resembles Saturnalia (which comes from the ‘Ischigualastian’ of Brazil). Thus the Elliot Formation is unlikely to be any older than the Early Norian (about 225 million years old). However this is a huge spread of time, about 42 million years in fact, can we narrow it down any further? Before we examine this question we need to dispel a common model for the deposition of the Elliot Formation which is often portrayed in the literature. This is the model of continuous deposition. This figure (taken from Holzforster 2007) is typical.

In this diagram the Elliot Formation is portrayed as filling the entire block of time between the Molteno and Clarens Formation. However this is not realistic. Deposition in the Karoo Basin was controlled by subsidence in response to tectonic activity in the Cape Fold Belt. Tectonic activity is rarely, if ever, continuously sustained over tens of millions of years. Further the sediments themselves show evidence being deposited in discontinuous pulses. The lower and upper members of the Elliot Formation represent two such pulses. Although no angular unconformity or extensive erosional surface separates these two members there is evidence that there was a non-depositional gap between the deposition of these two units. Firstly we have the wholesale changeover in fauna between the two members. There is no known vertebrate species or genus that occurs in both units. There are also lithological differences that indicate that the style of rivers crossing the floodplain had changed, from sinuous, deep permanent streams to shallow emphemeral braided streams. The latter seems to be coupled with a more arid climate which is also betrayed by other indicators of aridity such as the development of extensive calcareous paleosols, deeply muckcracked overbank horizons, and evidence of floodplain denudation during flash-flood events. Other features such as palaeocurrent indicators suggest that the overall direction of drainage also changed as did the source of the sediment. These features could have suddenly ‘switched’ but a time gap allowing these features to change more gradually seems far more likely.
So if we accept two pulses of deposition what age constraints can we put on them? There is little doubt now that the first pulse was Late Triassic in age. I’m currently preparing a paper describing rauisuchians from the Elliot Formation. They have been reported before but this will be the first time the identification will be based on diagnostic derived characteristics. If we accept that rauisuchians went extinct at the end of the Triassic then these occurrences certainly place the lower Elliot in the Triassic. But where in the Triassic? Geology can help us a little here. According to the model of Catuneanu et al. 1998 and Bordy et al. 2004 the deposition in the part of the Karoo basin where the Elliot Formation crops out occurred during an offloading phase when the Cape Fold mountains were shedding sediment after a mountain building event. During the offloading phase the more distal part of the basin (where the Elliot Formation lies) sags after bulging upward, creating accommodation space for the sediment to collect in.

The reciporical flexural model for basin development, as applied to the deposition of the lower Elliot Formation. Part of a figure from Bordy et al. 2004.

Structural and metamorphic geologists date the end of the mountain building event that is believed to have immediately preceded the deposition of the lower Elliot Formation to 215 million years, give or take 3 million years. This puts the lower Elliot in the mid to late Norian, maybe even extendig into the Rhaetian (depending how long the offloading phase lasted after the mountain building finished) as Randy suggested. Whatever its age I’m willing to bet that the lower Elliot Formation is more or less equivalent to the vertebrate-bearing horizons of the Los Colorados Formation based on similarities of their sauropodomorph faunas. These similarities include Lessemsaurus and Antetonitrus which are very, very similar (though a few telling differences do keep them as separate taxa, e.g. the proportions of metatarsal I). Eucnemesaurus (ex Aliwalia) is also extremely similar to one of the taxa lurking under the label ‘Riojasaurus’.
OK so that’s the lower Elliot, what about the upper Elliot? Here we don’t have ahelping hand from geology. A pulse of mountain building after 215 million years has not been detected (indicating it was a minor event).
Faunally the upper Elliot Formation contains taxa that seem to indicate an Early Jurassic age (e.g. the crocodyliform Protosuchus and a diversity of ornithischians) but this is rather weak reasoning. Nevertheless I think an age younger than the Hettangian one usually assigned to the unit can be supported on the following grounds:
1. The same biozone (the Massospondylus Range Zone)can be found from the beginning of the upper Elliot through to the top of the Clarens. Fossils are extremely rare near the top of the Clarens but Billy De Klerk of the Albany museum has collected a couple of good Massospondylus skeletons, that if I recall correctly, come from near the top of the Clarens. Basically the fauna of the Clarens is a depleted subset of what you find in the upper Elliot (easily explained by the limited sample from the Clarens). The only possible faunal change is that the little trithelodontid cynodont, Pachygenelus, might be replaced by a different trithelodontid, Diarthrognathus, in the Clarens. This suggests to me that we aren't dealing with a large span of time. Dinosaur genera seem to turn over every five million years or so, thus we are probably dealing with a duration in this vicinity for the entire upper Elliot to Clarens sequence.
2. The deposition of the Clarens is terminated by a sudden and precisely dated volcanic event - the eruption of the Drakensburg lavas which is dated to 183 million years.
3. There is no evidence of a time gap between the Clarens Formation and the volcanic eruptions. Indeed there is evidence that one followed the other without a hiatus. For instance in some localities lava flows can be seen to have filled the interdunal spaces in the Clarens dune desert. Clarens deposition seems to have continued after the eruption of the first few flows in some places. A great example can be seen on the road between Barkly East and Rhodes in the Eastern Cape. Lastly there is evidence that the volcanism was begining during the deposition of the Clarens - as is shown by the Clarens filled crater reported by Holzforster (cited in my last post). It would be great to get a date for the pyroclastic flows that form the basal layers of this crater but sadly no-one seems to have done it yet - any young geochronologist looking for a project?
4. So if we accept that the end of the Clarens can be precisely dated to 183 million years AND we only allow a duration of 5 million years or so for the Massospondylus Range Zone then the begining of the upper Elliot Formatio dates to the Early Pliensbachian (about 188 million years). Perhaps we could allow a few million years to have elapsed right at the end of the Clarens, before the volcanic lava flows began spilling out over the basin, and allow a rather long duration for the Massospondylus and its cohabitants but that would still only take us down into the late part of the Sinemurian.

There you have it. My guess is that the lower Elliot is mid-late Norian, there is a hiatus of about 15 million years before the upper Elliot and Clarens which probably span most of the Pliensbachian. How can this be tested? Detrital zircons would be a wonderfull source of data - once again any young geochronologists out there looking for a project?

references

Bordy EM, Hancox PJ and Rubidge BS (2004) Basin development during the deposition of the Elliot Formation (Late Triassic - Early Jurassic), Karoo Supergroup, South Africa. South African Journal of Geology, 107: 395-410.

Catuneanu O, Hancox PJ, Rubidge BS (1998) Reciporical flexural behaviour and contrasting stratigraphies: a new basin development model for the Karoo retroarc foreland system, South Africa. Basin Research 10: 417-439

Holzforster F (2007) Lithology and depositional environments of the Lower Jurassic Clarens Formation in the eastern Cape, South Africa.South African Journal of Geology, 110: 543-560.

Thoughts from the field: Welcome to Lake Drumbo

2008-12-10T05:55:00.000-08:00

I want to float some ideas based on some observations I've made in the field this year. So what have I been up to? Well firstly I've been poking my nose further south than I usually do. Most of the sites I've been working over the past half a decade are in the north end of the main Karoo Basin of South Africa. Here the dinosaur bearing Elliot Formation is relatively thin, probably because it lies over the solid Kaapval Craton, a big ancient continental block. This block probably prevented the basin floor from sagging too deeply during mountain building events off to the south (Tectonics is a VERY important factor controlling of deposition in the Karoo Basin). But down south you get off the Craton and the Elliot Formatin becomes thicker...over four times thicker. So with some money from Germany, and a collaborative team from Germany (led by Ollie Rauhut) and Great Britain, we began looking down south (mostly in the Eastern Cape Province). Despite the great thickness of sediment good outcrop is hard to find as the rainfall is quite high and vegetation rather thick.
Another rucurrent problem is figuring out where you are in the stratigraphy, these rocks don't come with labels!
So first a quick primer of the stratigraphy of the dinosaur bearing part of the Karoo.
The top of the sedimentary pile is usually referred to as the 'Stormberg Group' although this is not an officially recognised stratigraphic unit. The Stormberg Group consists of three formations: the Molteno, the Elliot and the Clarens. The Molteno is a series of coarse grained to conglomeratic sandstones, with fine grained siltstones, mudstones and coals in the south. It is rich in plant fossils (and some insects) but has not produced a single piece of bone - although there a some dinosaur tracks reputed to have come from this formation. The Elliot Formation marks the begining of the dinosaur body fossil record in South Africa. It is divided into two units: the upper and lower. At times it can be very difficult to determine in which unit you are in. The Elliot Formation is predominately made of red overbank muds and silts deposited on a humid (lower) to semi-arid (upper) floodplain. It would appear that the Elliot Formation covers quite a time range, with the lower member almost certainly being of Late Triassic age while the fauna of the upper member is very much Early Jurassic in aspect. The Clarens Formation consists of pale cream to white massive cliff-forming sandstones that are aeolian (wind blown) in origin. It records further aridification and the onset of a dune desert. Strangely the fauna doesn't seem to change much, if at all between the upper Elliot and the Clarens. You get pretty much the same taxa in the Clarens, just fewer specimens.
Now here is a parorama of the main valley wall on Upper Drumbo near Barkly East.

We excavated two dinosaur skeletons (Nelly and Charlie) from near the bottom of the Valley. You can see the cap of massive sanstone at the top of the peak in the centre (Castle Rock. This is clearly Clarens Formation. But where is the top of the Elliot Formation and where in the Elliot Formation do our dinosaurs come from?

At first glance the change in slope at the top of the valley seems to mirror the outcrop pattern of the boundary between the lower and upper Elliot Formations.

A colourised diagram of the outcrop of te Elliot and Clarens Formations. Note the change in slope between the two members of the the Elliot Formation. Modified from Bordy et al. 2004.
You can see this even better from a photograph taken from a higher vantage point looking across at Castle Rock, rather than up at it from the valley floor.

In this photo only the thick sandstone bench at the top of the valley can be seen. The smooth ramp-like slope leading up to Castle Rock is obvious. The mountains in the distance are made of the 2km thick pile of basalt that was extruded toward the end of the Liassic. You can read more about them here.
If this was the case then the upper Elliot Formation would form the smoother upper slopes leading to Castle Rock and our dinosaurs would be from the lower Elliot (hence Triassic). BUT one of them is almost certainly a Massospondylus (typical of the upper Elliot) and the sediments that enclose them are also typically upper Elliot in aspect. Perhaps everything from the base of Castle Rock to the valley floor is upper Elliot. Thats a verticle height of 210 m. The upper Elliot reaches thicknesses of 150 m down in the south, but 210m is a bit much. A few observations point me towards what I think is the answer. Firstly you will notice a thin bed of narrowly banded siltstone just below the big sandstones of the valley rim.

I've see a similar bed at the very base of the Clarens Formation in a number of locations (but not all). These are probably a series of playa lake deposits (about the only fossils you will find in them are little mussel shrimps or conchostracans) and they form a pretty good marker for the end of the Elliot.the smooth slope above the valley is not made of red overbank fines like the Elliot Formation. Further evidence that the upper slopes are actually within the Clarens Formation can be found if you actually climb up to them to take a look. The slope isn't made of red fluviatile mudstones, instead you will find thinly laminated pale creamy-grey shales. I've seen this lithology before - in small localised lenses of the Clarens Formation. They are interpreted as small interdune emphemaral pond, or playa lake deposits. However the thickness here (about 80 m) is, as far as I can find out, unprecedented. It seems to me that far from being a dune desert, this part of the world was host to a pretty large long lasting lake. Even more cool is that the same big package of shale can be found in near Blikana and at Rhodes. This may indicate a lake about 100 km across. Strange that I can find no mention of such an obvious feature in the literature. So what lived in or or around it (assuming my interpretation is correct? Bugger all I'm afraid. You won't find even scattered fish bones or scales. My guess is that it was very shallow, hypersaline and prone to frequent drying out. Much like Lake Eyre in the Tirari Desert of South Australia. Indeed given that it is surrounded by a dune desert and the northern section of the Lake is about the same size as the lake I'm suggesting, Lake Eyre makes a pretty good analogue.

Lake Eyre

However there IS a report of a large Lake in the Clarens Formation off to the South West of this deposit. However this lake is an altogether different kind of thing. Holzforster (2007) reports on lacustrine deposits in the Clarens Formation in the Exterem South West end of the outcrop of the Formation. However here the Clarens is incised down into the Elliot Formation, and the lake deposits are underlain be thick pyroclastic deposits. In other words this south-western lake was developed in a volcanic crater. Sadly no fossils have come from here either, - its a pity because a late Early Jurassic Liaoning-style lagerstatte would be sooo cool.

references

Bordy EM, Hancox PJ and Rubidge BS (2004) Basin development during the deposition of the Elliot Formation (Late Triassic - Early Jurassic), Karoo Supergroup, South Africa. South African Journal of Geology, 107: 395-410.

Holzforster F (2007) Lithology and depositional environments of the Lower Jurassic Clarens Formation in the eastern Cape, South Africa.South African Journal of Geology, 110: 543-560.

Field trip photos

2008-12-09T04:27:00.000-08:00

I'm currently writing up a report on the lightening quick field trip I took at the end of November for this blog but am getting delayed by all sorts of real-world duties. So for now I'll just show-case some of the pictures.

Matthew Yates assists Charleton Dube and Sifelani Jirah in excavating a dinosaur tail.

The tail of 'Charlie' the sauropodomorph (yes another one!) emerges

Upper Drumbo, type locality of Dracovenator regenti, and site of 'Charlie'. Casle Rock is in the background but where is the contact between the Elliot Formation and the Clarens Formation?.

Comments

2008-12-01T22:06:00.000-08:00

Mea Culpa, I didn't realise the comments were only letting google users have their say. I'm sure when I set this up I allowed comments from everyone. Anyway the problem is fixed - I invite comments from anyone.

Two new Fossil Cowries

2008-12-01T03:56:00.000-08:00

A small paper has just been published on two new fossil cowries from the Miocene of South Australia (Yates 2008). Although it is unlikely to set the palaeontological world on fire it is a personally satisfying paper as it represents my first published foray into a subject area that has actually been close to me for most of my life. As I have mentioned before growing up in South Australia provided next to nothing in the way of actual dinosaur digs or even museum displays of dinosaur bones. If you wanted to get out and dig for your own fossils then the marine limestones and marls of the River Murray cliffs was about the only game in town. Most of these sediments are rather coarse grained calcarenites that unfortunately offered no protection ravages of groundwater which dissolves shells made from aragonite (the form of calcium carbonate that the majority of molluscs use). As a consequence nearly all mollusc fossils are present only as moulds surrounding the void where the shell once was. There is a gleaming exception: a silty marl unit called the Cadell Formation (formerly the Cadell Marl Lens of the Morgan Limestone).

The Cadell Formation in outcrop (note the house boat on the river channel in the background).

The Cadell Formation in context. The creamy coloured beds (largely grassed over) are the Cadell Formation while the strongly banded orange limestones above it belong to the Bryant Creek Formation.

This formation is packed with aragonitic mollusc shells, sometimes so well preserved they look as if they have freshly come off the beach. The extent of the shelly facies of the Cadell Formation is quite limited, the main exposure stretches for just over 10 km between the towns of Murbko and Morgan, however for most of this length the exposures form sheer cliffs that plunge straight into the river. Only one decent access point exists, at the type locality for the formation, about 6km south of Morgan. This site is well-known and collectors have visited it for over a century. The first thorough documentation of the fossils of the Cadell Formation were published by Ralph Tate, a British born geologist, palaeontologist and botanist who emigrated to South Australia, and became the head of the Department of Geology at the University of Adelaide. Incidentally the Tate medal is still awarded each year to the best honours research project in the department for that year. In 1994, yours truly was the recipient of this award, definitely one of the proudest moments of my life, not least because Tate with his extremely broad knowledge of natural history was a personal hero of mine. I was very surprised to learn, while googling around for details of the man’s life I found that he and I share the same birthday.
Anyway back to the Cadell Formation, one would think that with such a long and venerable history of study and collection, there would be little left to discover. Not so; the mollusc fauna has not received a comprehensive survey since Tate’s pioneering work and the paleoenvironment of the Formation remains an enigma. I first visited this site when I was just 13 years old and fell in love with the site. I visited the site several times a year until I finally left Australia when I was 28. Over the years I’ve amassed a collection that includes more than 200 species of mollusc. Many of these are new records for the formation, and several represent new species. However as my academic career took me into vertebrate paleontology and dinosaur research, I left my interest in these mollusc fossils lie dormant but not forgotten. Late last year I finally got my chance to produce my first publication in this field. I hope many more of greater significance will follow. The paper outlines two new species of cowry from the Cadell Formation that were formerly thought to belong to middle Miocene species from the mollusc-rich basins to the east in Victoria. The first of these is Umbilia caepa, an extraordinarily fragile member of the basal cowire genus Umbilia.

Umbilia caepa

Umbilia was featured on this blog here and here. U. caepa is quite similar to the Victorian contemporary species U. leptorhyncha but consistently differs from it in a number of respects including the weaker apertural dentition, the development of a plate-like posterior columellar callus bordering the posterior canal and broad plate-like flanges on each side of the anterior rostrum. It also has a more strongly developed pyriform shape which resembles the bulb of an onion (hence the name). Of course with palaeontological samples it would have been impossible to demonstrate that U. caepa was a reproductively isolated from the eastern U. leptorhyncha or was simply the western end of a clinally variable species. However much to my surprise that when sorting through the various fragments from the Cadell Formation I found a small thin piece of Umbilia that does indeed have strong apertural dentition and weak lateral ridges on each side of the anterior rostrum (as opposed to broad flanges) amongst other features that indicate it was actually a true U. leptorhyncha. No intermediate specimens could be found indicating that the two species were sympatric in the Murray Basin but only U. leptorhyncha extended east into Victoria.
The next species I described belongs to the endemic southern Australian clade Austrocypraea, which is now regarded as cold-water adapted subgenus of the large tropical Indo West Pacific genus Lyncina (this includes the famous ‘golden cowry’ Lyncina aurantium) based on molecular evidence (Meyer 2003).

Lyncina aurantium image from en.wikipedia.org/wiki/Cypraea_aurantium

The species, which I called L. (A.) cadella, is abundant at the site and many specimens had been found and examined by previous researchers but had not received its own name due to a particularly bad tangle of taxonomic confusion surrounding the species.
Tate had found this species but had regarded as a mere variant of the Victorian species L. (A.) contusa. In a similar case to U. caepa, L. (A.) cadella is close to L. (A.) contusa but consistently differs from it in a number of respects relating to size, dentition and shape of the fossula.

Lyncina (Austrocypraea) cadella

As there are consistent differences between the two populations I think that the South Australian population is deserving of separate species status. Frank Schilder thought so too, when he revised the Australian fossil cowries in 1935. Schilder was a dedicated cowry researcher, and it is a testimony to his deep knowledge of the group that much of his generic classification of these extremely conservative and homoplastic shells was upheld by recent molecular phylogenic work. Sadly his work on Australian fossil cowries was not among his better efforts. The main problem was that he was working from collections held in Europe that were rife with poor locality data, leading to all sorts of confusion. To cut a very long story short Schilder described L. (A.) cadella -twice! – using two different names, neither of which are available. In the first instance he confused his own specimen of L. (A.) cadella with an Eocene species named by Tate – ‘Cypraea’ ovulatella and referred it that species using the combination ‘Austrocypraea ovulatella’. But ‘C’ ovulatella (now Willungia ovulatella) clearly isn’t the same thing as L. (A.) cadella, it isn’t even a cowry! (the confusion was the result of relying only on illustrations and an icorrect locality label). Secondly he described a second sample of L. (A.) cadella that was obtained directly from Tate himself by the French malacologist Alexandre Cossmann as a new species ‘Austrocypraea subcontusa’. So the species from the Cadell Formation should be called L. (A.) subcontusa right? Wrong. In an inexplicable move after describing the Cossmann’s sample Schilder selected an aberrant dwarfed Victorian specimen as the holotype of his new species. After looking at the Victorian specimens I’m convinced that the holotype of Austrocypraea subcontusa is just an extreme variant of true L. (A.) contusa. It still differs from L. (A.) cadella in a number of respects and can be connected to typical L. (A.) contusa by a number of intermediates. The upshot of all this is that the common species of Lyncina (Austrocypraea) from the Cadell Formation has never received a valid scientific name despite being known for well over a century.
So what is the significance of all this arcane taxonomy? The main significance is that these species are more evidence of faunal differentiation between the various Miocene epicontinental basins. This is in contrast to the modern molluscsn faunas of southern Australia where most species have broad ranges stretching across the entire southern Australian seaboard. Although there certainly were many widespread middle Miocene species in southern Australia there does appear to have been higher levels of endemicity, perhaps fueled by the presence of restricted epicontinental basins and the propensity for many southern Australian molluscs to abandon the planktonic dispersal stage of their development.

Adam Yates (2008). Two new cowries (Gastropoda: Cypraeidae) from the middle Miocene of South Australia Alcheringa: An Australasian Journal of Palaeontology, 32 (4), 353-364 DOI: 10.1080/03115510802417927

C.P. Meyer (2003) Molecular systematics of cowries (Gastropoda: Cypraeidae) and diversification patterns in the tropics. Biological Journal of the Linnean Society 79: 401-459.

Closing in on turtle origins

2008-11-27T23:11:00.000-08:00

I wrote in this blog in October that we can expect a more complete prototurtle. Never would I have dreamed that it would appear so quickly and that it would be even more primitive than Proganochelys or Chinlechelys. Finally something that hasn’t progressed so far down the road to turtlehood that its ancestry has been all but erased. Named Odontochelys semitestacea, it came as quite a shock to me – why? Because of all the competing hypotheses of turtle origins this guy seems to support the one I found the least convincing – that is turtles are the sister group of sauropterygians (an aquatic group of diapsid reptiles including placodonts, nothosaurs and plesiosaurs). My own musings that aetosaurs might be related to turtles now seems very unlikely indeed. It will take time for the remains of Odontochelys to be hashed over (the announcement paper is somewhat light on anatomical detail) to really determine what origin theory it supports. However I think we can now confidently rule out a the pariesaurian hypothesis. Of the synapomorphies linking pareiasaurs, or derived subclades within pareiasaurs, to turtles a good many of them are missing in Odonotochelys. These include: basal tuberae (ventral swelling of the braincase) midway between the occipital condyle and the basipterygoid processes (where the palate attaches to the braincase); acromial process on the scapula, closure of the spaces between the ribs (it is debatable wether or not any turtle actually has this condition); fewer than twenty caudasl vertebrae; and body covered in united osteoderms. Note that although it appears to support a diapsid origin for turtles the skull of Odontochelys lacks any trace of temporal openings so perhaps we can't quite rule out other anapsid sister groups just yet.

Not a part of the turtle sister group, the pareiasaur Bradysaurus. Image from wikipedia commons

Odonotchelys is yet another gem from the palaeontologically rich nation of China, this time from the marine Triassic deposits of the Guizhou Province, which are famous for their diverse Marine reptile fauna. One last note on the dating. The age of Odontochelys is given as about 220 ma based on biostratigraphy which places the unit it comes from in the Lower Carnian. As discussed recently by Bill Parker over at Chinleana the dates for the Triassic have been substantially revised of late, and if a lower Carnian age is to be upheld for Odontochelys then its absolute age is probably closer to 235 ma.

Chun Li, Xiao-Chun Wu, Olivier Rieppel, Li-Ting Wang, Li-Jun Zhao (2008). An ancestral turtle from the Late Triassic of southwestern China Nature, 456 (7221), 497-501 DOI: 10.1038/nature07533

The giant pineal 'eye' of Platycyclops

2008-11-20T23:49:00.000-08:00

The answer to the the little photo quiz was as the title suggests the relatively enormous pineal foramen of the oudenodontid dicynodont Platycyclops - so kudos to Matt. Quite why these dicynodonts have such enormous pineal openings is an unanswered question. Modern mammalian pineal glands are buried deep in our grossly inflated brains but are still used to regulate day/night cycles and seasonal cycles. In mammals it is influenced indirectly by exposure to light via signal that originate from the retina. In other vertebrates with a pineal foramen direct exposure of the pineal itself triggers the pineal gland to secrete its regulatory hormones. Pinealocytes have a strong resemblance to retinal cells and it is certainly tempting to speculate that the pineal organ of Platycyclops and related dicynodonts had crude image forming abilities. The forward tilt of the opening certainly gives the impression of a third 'eye'.
Googling around for information turned up one other little factoid, the name Platycyclops Broom 1932(the dicynodont) is a junior homonym of Platycyclops Sars 1914 (a copepod crustacean). As far as I know no-one has proposed a replacement name for the dicynodont.

Picture of the Day: long tailed widow bird

2008-11-16T23:39:00.000-08:00

Just a quick post while I'm on leave - I'll be revealing the mystery orifice soon, so keep guessing - one of you is very close. We took a family outing to the rhino and lion park in ‘The cradle of humankind’ a world heritage area that includes the famous Sterkfontein and Swartkrans caves where several australopithecines have been found. While there I managed to get this shot of a breeding male long-tailed widow bird (Euplectes progne), the epitome of an elaborate sexual display that is a major handicap to its owner. Non-breeding males are drab, brownish, sparrow-like birds with tails of normal length.

What is it?

2008-11-11T02:47:00.000-08:00

Yes, another round of 'what is it?' I'm off on leave for a week. I hope I can post something in the during this time but in case I don't have a go at guessing the identity of this osteal orifice. Clue: it has nothing to do with any sort of sauropodomorph (for once). Oh the scale bar represents 2 cm.

Defending the indefensible

2008-11-07T06:26:00.000-08:00

A couple of weeks back there was a fresh round of bashing on poor little Pantydraco. Bashing the name, not the dinosaur that is. It is a matter of some embarassment to me that I should be tied to what is widely regarded as the worst dinosaur name ever. I take pride in the names I craft, and I don't think I'm too bad at it (Dracovenator, Antetonitrus, Nanalania are some faves) even if I do say so myself.
So here is some of the backstory behind the name. Firstly: it was not my invention! That particular dubious honour goes to Peter Galton. When I first named the species caducus I found some characters that linked it with what I was calling (and still call) Thecodontosaurus antiquus, so thought that the wisest course of action was to name a new species in that genus. However as I found out more about Thecodontosaurus antiquus (and I regard all of the English cave fill sauropodomorphs as one taxon) more and more differences with the Welsh ‘Thecodontosaurus ‘ caducus started to show up. For instance the ischial shafts of T. antiquus are an unusal flattened ovoid cross-sectional shape whereas those of ‘T.’ caducus have the classic triangular cross section seen in most other basal sauropodomorphs. Significantly support for a monophyletic Thecodontosaurus had diminished to the point that it was no longer recovered in all of the most parsimonious trees of my improved cladistic analyses (as more characters were added and more scorings were based on first hand observations) . So I had come to the conclusion that it was time to erect a new genus for ‘T.’ caducus. I even had a tentative name thought up – Cambrambulus – the Welsh wanderer. However I was not quick enough and at the 2005 SVP Peter Galton told me that he was close to submitting an MS giving caducus that infamous generic name.
Naturally I felt rather attached to the first dinosaur species that I named and wanted to remain associated with the generic name (which after all is the most frequently cited name in dinosaur circles). So I told Peter about my plans and we agreed to write the paper together, even though our reasons for naming the new genus were different. Peter felt that Thecodontosaurus was a dubious name because he thought that the type specimen of T. antiquus (the type species of the genus) was indeterminate. I agree that it isn’t the best and that it has no single derived character that cannot be seen in other sauropodomorph taxa. However I am still unconvinced that there are two morphs in the original Durdham Downs quarry, or that Asylosaurus is all that distinct. Taken collectively the Thecodontosaurus antiquus sample is unique and diagnosable. The utility of bone bed taxa is itself the subject for another post but to put it simply I’m all for using them in the right circumstances. In this case the surviving scanty sample from Durdham Downs is backed up by a large sample from Tytherington . This is another set of sauropodomorph bones from a fissure fill in the English south-west. Here there is absolutely no sign of two morphs and all of the recovered bones are virtually identical with those from Durdham Downs.
So there we are, the Pantydraco paper is very much a compromise - melding two different viewpoints but agreeing that little caducus needed a new generic title. Perhaps I should have pushed Peter to change the name, but being my meek and mild self, didn't do so. In anycase I didn't think it was quite that bad at the time,although yes, I was quite aware of the conotations (I guess thats a little bit of my juvenile sense of humor showing though).
Lastly for all those who absolutely hate the name - remember it is correctly pronounced 'Pant - uh - dray - co' which is not quite so bad as 'panty'.

From the galleries of the BPI: The Cape Giant Zebra

2008-11-05T01:31:00.000-08:00

This specimen is a partial set of jaws of Equus capensis, the so called cape giant zebra, from Makapansgat, the most northerly australopithecine site in South Africa. Actually, although robust these equids are not so giant, being about the size of a big modern horse. Fossils of this robust equuid are widespread throughout South Africa, with the type coming from close to Cape Town, way down in the southwest.
It is often said that Africa escaped the megafaunal extinctions of the late Pleistocene but there is a definite set of large African mammal species that clearly did not make it through to the present. These include the giant buffalo Pelorovis, other bovids like Megalotragus, and supposedly Equus capensis. But if Charles Churcher is right reports of E. capensis' demise are greatly exaggerated. It s apparently alive and well in the form of.... Grevy's Zebra.

Image from wikimedia commons

Apparently the teeth (which are what most extinct Equus taxonomy is based on)of E. capensis do not differ in significant ways from those of E. grevyi and a bunch of east and northern african fossil equiids (e.g. E. oldowayensis).
Grevy's zebra is now restricted to East Africa and cannot be found anywhere near Suth Africa. So if it doesn't represent an actual extinction it does represent a drammatic range contraction.

reference

Churcher CS (2006)Distribution and history of the Cape zebra (Equus capensis) in the Quaternary of Africa. Transactions of the Royal Society of South Africa 61:89-95

What was it?

2008-11-04T05:10:00.000-08:00

That ugly mystery bone is out now. What a disaster! when lifting it from its jacket, an undetected puddle of glue had soaked through the sepparator and firmly welded the underside to the jacket (lesson for the future - make sure there are several layers of sepparator between the bone and the jacket). The remarkable thing about the bones from this quarry is that although the compact outer bone is well-preserved the interior is like compressed flour. Once a break is started the whole bone tends to crumble to powder, much like the unravelling of a woollen jumper once the stiching comes undone in one place. Consequently the finished product is not one of our lab's proudest moments and I won't be showcasing it here. Nonetheless two things are apparent 1) it is a busted ischial peduncle from an ilium - exposed in medial view in the photo. 2) this part alone is about the same size as a middling Massospondylus, so although Rutger was halfway right he doesn't get full marks. The diagram below indicates which part of the ilium the bone is, and should give the astute clues to where I think its relationships lie (incidentally it is from the same site as the sauropod caudal I described in the South African Journal of Science (2004, vol. 100. 504-506)

End of year blues

2008-10-29T01:48:00.000-07:00

Hi guys,

This blog has become far more quiescent than I ever intended it to be. I am currently feeling exhausted and swamped by marking at the end of the year, including honours projects, exam papers and essays - urgh. Of all my duties I hate marking the most. Time is of the essence but I want to be scrupulously fair to all, a desire that used to compell me to read and re-read each essay two or three times before finally settling on a mark. When not marking I am tidying up various other bits of end of year business - and occasionally writing up some of my research for publication. I wish I could tell you guys about it (it is one of the most enjoyable aspects of my job) but sadly this work has to go through the long drawn out process of peer-review and publication first. Maybe I'll be able to say something in 2010!
Anyway I've dragged up a picture of an old field trip from my vaults. You can see that the weather was kind of .... damp. This happened a lot on my field trips (and not always in rainy season either) so much so that one of the dinosaurs we happened to find in between rainstorms received the nickname 'Rainmaker'.
Anyway the load on shoulders should be lifting soon. I'll have a visit from my mum soon and we'll be doing a few trips round Gauteng. Then I'll be off on a short field trip to retrieve a dinosaur we left behind earlier in the year. So by December my batteries will be recharged and blogging will begin with renewed vigour (I hope!)

What is it?

2008-10-21T03:02:00.000-07:00

...... The answer is - I don't know. This is one of those weird 'head scratchers' or GOKs (God only knows) that we get from time to time. Celeste is prepping it up right now. Its been sitting down in the lab for over two years and various volunteer preparators have had a go at it and quickly left it for easier more exciting projects. It comes from the upper Elliot Formation in a quarry that has produced more than one type of sauropodomorph as well as a protosuchian crocodile and some honkin' big theropod teeth. Any suggestions?

Good News Everyone!

2008-10-10T00:47:00.000-07:00

After spending the whole week in hospital (it wasn't just tonsilitis after all) Matthew will probably be coming home tomorrow ..... and one of palaeontology's holy grails - a basal stem turtle has been found and published.

I imagine most of my readers know that pinning down the closest relatives of turtles and the origins of their bizarre morphology has been one of the most recalcitrant problems in tetrapod evolution.
While the lack of holes in the cheek region of the skull suggests that they are an offshoot of the anapsid reptiles, with procolophonoids or pareiasaurs being the main contenders, more than one large scale morphological cladistic analysis has found that turtles are members of the Diapsida (derived reptiles with two pairs of holes in the temporal region of the skull). Molecular work also supports a diapsid origin for turtles but tends to place them close to, or within, the Archosauria (crocodilians, dinosaurs, birds and their kin)whereas the morphological work tends to align them with the Lepidosauromorpha (lizards, snakes and kin).

Sadly the new turtle described by Walter Joyce and colleagues in Proceedings of the Royal Society is too fragmentary to really speak to this vexatious issue. But it does tell us quite a bit about how their most distinctive feature - their shells - evolved and lets us know that the answers are out there (given the recent spate of excellent discoveries in the Chinle and its equivalents I'm sure a more complete proto-turtle won't be be a long time coming).

But first a little of the who, what where and when. The new fossil is called Chinlechelys tenertesta (the thin shelled turtle from the Chinle)and the known remains consist of fragments of shell with attached underlying parts of the vertebrae and ribs and isolated osteoderms found in the Bull Canyon Formation of New Mexico. The name is taken from the Chinle Formation, which is a little odd since most stratigraphers and palaeontologists would not to place the Bull Canyon Formation in the Chinle Formation (or Group according to some), prefering instead to place it in the Dockum Group. The age of this part of the Dockum is probably mid-late Norian of the Late Triassic, somewhere between 210 and 219 million years old.
There are other equally old turtles in Europe, Greenland and South America but none so primitive in shell design as Chinlechelys. For starters its shell is unusually thin but more importantly it still has rather individualised ribs, that although joined to the inside of the shell, are not fully subsumed into it.
The telltale fragment - a piece of shell with an individualised rib beneath it.Modified from Joyce et al. 2008

This is important because it helps falsify the model that the shell is a modified ribcage alone and supports the hypothesis that the shell is a composite structure formed from the agglomeration of trunk vertebrae, ribs and several rows of osteoderms (bony armour in the skin). Intriguingly modern developmental studies have suggested the former hypothesis because it appears that the shell grows as part of the endoskeleton (that is it is made of replacement bones that are preformed in cartilage and derived from scleritomic mesodermal cells. Developmental studies can yeild powerfull evolutionary data but I think the takehome message here is that developmental pathways can and do evolve. Palaeontology definately still has a place at the high table of evolutionary studies!
Hypothetical steps in the evolution of the turtle shell following the osteoderm hypothesis. From Joyce et al. 2008

Bonus musing: If the molecular data are correct it is perhaps no co-incidence that some pseudosuchian, or crurotarsan - whatever you preference, archosaurs have rather turtle-like carapaces. Aetosaurs even have a plastron of plate-like osteoderms.
Paratypothorax, an aetosaur. Compare to hypothetical stage II above. Image from www.dinotime.de

WG Joyce, SG Lucas, TM Scheyer, AB Heckert, AP Hunt (2008). A thin-shelled reptile from the Late Triassic of North America and the origin of the turtle shell Proceedings of the Royal Society B DOI: 10.1098/rspb.2008.1196

Tonsilitis again!

2008-10-06T03:52:00.000-07:00

My little guy, Matthew, who is one month shy of his second birthday, has come down with serious tonsilitis for the second time in as many months. It would appear to be a law of nature that kids always fall sick on a weekend, usually a Sunday evening when medical services tend to be a little thin on the ground (especially for those not wishing to sit in a casualty waiting room for hours). At the moment this is my main blog-writing time. So sadly I'm empty handed - once again. I don't feel to bad about this however because I managed to get hours of research writing in, before Matthew got sick.
In lieu of my own work I would like to point folks to Matt Wedel's thorough dissection of the recent Aerosteon paper.

Matthew in better health doing some computer work of his own.

Umbilia gazing - part II

2008-09-29T02:51:00.000-07:00

We last left off our survey of Umbilia in the middle Miocene where we looked at U. eximia the most abundant and widespread species.
Two of the remaining four described middle Miocene species are some of the weirdest of all crown-group cowries (I say crown group because there were some truly bizarre looking stem-group cowries, e.g. Gisortia).

U. siphonata (above) is one of these. It is a very large cowry, attaining a length of almost 17 cm, which is not far behind the biggest specimens of Macrocypraea cervus, the largest extant cowry, which used to reach sizes of 19 cm in length. However U. siphonata is cheating a little since the anterior and posterior rostra of this species are produced into great upwardly curving ‘horns’. The rudimentary flanges that support the bases of each rostrum of U. eximia are much better developed in this species. Even stranger is U. gastroplax, the ‘flanged cowry’ (specimen on the left is from Darragh 2002). This species also has elongated horn like rostra, although they are not as long as in U. siphonata. However the flanges have expanded outwards, merging together and making a continuous brim that encircles the entire base of the shell. The result looks much like a snow-shoe. Indeed it has been suggested that this is exactly what its function was and that it was an adaptation to living on soft, ‘soupy’ bottoms. One wonders then if U. siphonata was adapted to the same conditions but simply didn’t bother to keep itself on top of the sediment surface, and used its long rostra to carry its siphons up into clear water.
The fourth middle Miocene Umbilia we will look at is little U. leptorhyncha (below). Although common and widespread, good specimens are rare due to the thin-shelled fragility of this species. This species is a departure from the other mid Miocene species in its small size, globose shape and poorly developed rostra. In these respects it most closely resembles U. prosila and may be closely related to it.

All of these species can be found in both South Australia and Victoria (U. gastroplax has not been officially recorded from South Australia but I have personally collected two specimens from the Cadell Formation on the banks of the River Murray)
Darragh recorded the extant U. hesitata as a fifth middle Miocene species, albeit one that only appears at the end of the stage, with little to no time overlap with the previously mentioned species. The taxonomy of these rare later middle Miocene Umbilia is a complicated issue. Two species have been named Umbilia tatei and Umbilia cera. Both are short , with weakly developed beaks and heavily calluses surrounding the basal margins and probably represent the same species whatever they are. Problematically if these really are small specimens of the extant ‘wonder cowry’ (as U. hesitata is sometimes called) then we have the problem that U. tatei would have priority over U. hesitata. I’m sure all the avid cowry collectors would object to replacing the entrenched U. hesitata with U. tatei. Fortunately I don’t think they have to. Although U. hesitata does display a range of adult sizes which overlaps with the small shells of U. tatei, small modern U. hesitata resemble typical large specimens more than they do U. tatei. In particular no modern U. hesitata has such thick marginal calluses as U. tatei, nor do they develop the elongate coarse dentition seen on the holotype of U. cera (these are not present in the types of U. tatei but the dentition of these specimens appears to be underdeveloped due to immaturity).

A late Miocene U. 'hesitata', probably belonging to U. tatei.

From the late Miocene and Pliocene (there is no Pleistocene record of Umbilia at all) there is just a single species, the extant U. hesitata (although some of these are a little different from modern U. hesitata while others probably belong to U. tatei). Then in our modern seas we find five species: U. hesitata, U. armeniaca, U. capricornica, U. orriettae and U. petillirostris.
However unlike the middle Miocene where you can find up to four species at the same locality almost all of the modern species have mutually exclusive ranges (only U. capricornica and U. petillirostris overlap in the deep Capricorn Channel of the Great Barrier Reef. Moving anticlockwise around the Australian coast we find U. armeniaca (Western Australia to Kangaroo Island, South Australia), U. hesitata (south eastern South Australia to Southern Queensland), U. orriettae (Moreton Bay, Queensland) and U. capricornica/U. petillirostris on the Great Barrier Reef. It is interesting to note that this pattern matches the phylogenetic pattern recovered in a comprehensive molecular phylogenetic analysis of modern cowries (Meyer 2004). In this analysis U. armeniaca was the sister group to all other living species and U. hesitata was the sister group to U. capricornica + U. petillirostris (U. orriettae was not included but morphologically it appears to be intermediate between U. hesitata and U. capricornica). Thus the modern forms appear to be the result of a radiation that proceeded from west to east. All of these living species are rather similar to one another and have a rather generalised shell structure compared to the excesses of the middle Miocene.

Umbilia hesitata, the most abundant extant species.

Most specimens display a moderately well-developed posterior rostrum and have highly reduced anterior tubercles that are separated by an oblique sulcus. These characters suggest that the modern taxa are more closely related to U. eximia and U. tatei than any of the other extinct species. However the type specimens of U. petillirostris stand out as something unusual. Unlike other living Umbilia the types of U. petillirostris are globose and thin-shelled with a very short posterior rostrum. In these respects U. petillirostris resembles the smaller middle Miocene species, U. leptorhyncha and the late Oligocene U. prosila. Darragh (2002) suggested that these three species represented a lineage that had been separate since the Oligocene. But using the molecular phylogeny this would suggest that all of the modern species have been separate since at least the late Oligocene, despite sharing a similar hesitata-like morphology that does not show up in the fossil record until the late Miocene. However I strongly doubt that U. petillirostris is closely related to U. prosila and U. leptorhyncha. Despite its globose shape and thin shell it displays characters typical of the modern clade such as large size, a moderately produced posterior beak, and weak anterior tubercles. A greater sample of specimens shows that U. petillirostris and U. capricornica are quite variable and that individuals of each species can be found that approach the other in morphology. Indeed some have suggested that the two species are not distinct at all (Wilson and Clarkson 2004). Nevertheless limited genetic sampling does indicate that U. petillirostris does maintain a distinct haplotype (Meyer 2004). Excellent photographs of all the living forms can be seen here.

Next week: the origin of Umbilia.

References

Darragh, TA (2002) A revision of the Australian genus Umbilia (Gastropoda: Cypraeidae). Memoirs of the Museum of Victoria 59: 355-392.

Meyer CP (2004) Toward comprehensiveness: increased molecular sampling within Cypraeidae and its phylogenetic implications. Malacologia 46: 127-156.

Wilson B, Clarkson P (2004) Australia's Spectacular Cowries: A Review and Field Study of Two Endemic Genera-Zoila and Umbilia. Odyssey: El Cajon, 369 pp.

Lookin' out my back door

2008-09-24T03:35:00.000-07:00

Well out my back window actually. We've been watching this industrious little guy for almost three years now. He is a masked weaver (Ploceus velatus), and in order to attract a mate he has to construct a nest of sufficient quality to encourage a female to lay her eggs in it. Sadly he's a bit of a loser. Although several females have checked him out he has never been able to seal the deal. After every rejection he would demolish the nest and start again. Now however it appears he is so riddled with frustration and self-doubt that he just builds and destroys nest after nest without even getting it looked at first. I kind of empathize with him, my early years (15 through to 26) weren't too dissimilar.

More sauropod vertebrae/ ceratopsian frill convergence

2008-09-22T02:31:00.000-07:00

I was reminded by Mike Taylor's recent post, noting that a Camarasaurus vertebrae seems to have a ceratopsian frill growing out of it, that I had had the exact same thought when I saw 'Max'. Max is a diplodocid (identified as Apatosaurus but I have my doubts) found by the crew at the Saurier Museum in Aathal. However this time the 'frilloid' process is composed of the two postzygapophyses and the perforate interpostzygapophyseal lamina. Incidentally the interpostzyg laminae of most of Max's cervicals are similarly perforate. It is a real feature, not caused by damage - weird huh?

The last dicynodont

2008-09-18T02:36:00.000-07:00

With so much going on I've had little time for blogging. Recently there was some discussion of the supposed Australian Cretaceous dicynodont (maxillary fragment of the specimen is pictured on the left) over at Chinleana. I'll add my two cents here rather than commenting there just to keep something ticking over on my blog. Randy Irmis made a startling comment that the consensus was that it was indeed a dicynodont. This is news to me, I had always thought that the identity of the specimen was always the weak part of the claim. I have to add that I've never seen the specimen myself. Randy goes on to add that because it was surface float it is the provenance of the specimen that is suspect. Here I have to add my voice in support of Thulborn's original assesment, whatever it was there can be little doubt that it came from the Cretaceous. As has been noted Australia is flat and rather geologically quiescent. The nearest Triassic rocks are many hundreds of kilometres away. Nor do these Triassic rocks have much in the way of dicynodonts in them anyway - just one beat-up quadrate from more than 20 years of intensive collecting in the Arcadia formation (the main fossil-bearing Triassic formation of south-eastern Queensland). When you are out prospecting in most parts of the world you almost never find fossils more than a few tens of metres from the formation that bore them (unless there is a transport mechanism such as a river). Australia certainly never had post-Triassic glaciations that can randomly transport objects over large distances. So if the morphology is definately saying dicynodont then hey, I'm prepare to accept this extraordinary claim. Indeed recently another clade thought to have died out before the end of the Triassic has been found to have survived until the Cretaceous (I can say no more) so survival of the Dicynodonts may not be so weird after all.

The lizard biters

2008-09-09T02:03:00.000-07:00

The answer to the puzzle is that both were named Saurodectes, meaning ‘lizard biter’. One is an insect from the Early Cretaceous of Siberia, while the other is an early Triassic procolophonoid parareptile found in South Africa. I was part of the team that found the procolophonoid although I can’t claim that I found the specimen. In fact I found precious little while Ross Damiani found 'Saurodectes' despite being severely hampered by a broken ankle. Some people are just gifted when it comes to field-work and I am not one of them. The insect has priority over the name and we had to rename our procolophonoid Saurodektes (Modesto et al. 2004). Not that there is much shame in proposing a name that is preoccupied by an arthropod. With so many arthropods it seems to happen all the time. I got my first look at the real Saurodectes when I purchased Grimaldi and Engel’s magnificent tome ‘Evolution of the Insects’. And what a fascinating insect it is.
Described as a kind of louse, Saurodectes vrsanskyi (Rasnitsyn and Zherikhin 1999) has an unusual set of characters. Some of these such as the single claw at the end of its legs, short, widely spaced legs and membranous distensible abdomen are typical of ectoparasitic insects but the very large eyes and lack of spiny setae are not. What those handle-bar like structures sticking out its head are is anybody's guess. A recent survey of fossil lice could not find any convincing characters that definately placed the fossil amongst the lice (Pthiraptera) but could not suggest any alternative relationships either (Dalgleish et al. 2006).

The head of Saurodectes, from Grimaldi and Engel (2005).

The original describers (Rasnitsyn and Zherikhin, 1999) suggested that it was a pterosaur parasite on the basis that it was too big at 17 mm to parasitise Mesozoic mammals but had single clawed feet like modern mammal lice. This is seen as an adaptation to gripping hair shafts, and that since pterosaurs were also hairy then it was supposed that Saurodectes plied its way through ptero-fuzz. However I don’t see a close correspondance between the claws of modern mammal lice and those of Saurodectes. Actually this is not the only weird Mesozoic insect that has been claimed to be a pterosaur parasite. Sauropthirus longipes, a scorpionfly relative from the same formation as Saurodectes has also been hypothesized to have found its living on pterosaurs. Actually the stiff, backwardly pointed spines and eyelessness of this insect seems to be more fitting with this kind of lifestyle. It is, of course, not impossible for both of these to be pterosaur parasites but it strikes me that some of the odd features of Saurodectes may be explicable if it lived on the scaly hide of a large non-feathered dinosaur. In modern lice there is a loose correlation between parasite size and host size indicating that Saurodectes had a large host. Furthermore backwardly pointing setae may be of little use on a host that lacks filamentous integument. Eyes may also be of use to a large, exposed ectoparasite, not sheltering under a dense pelt of hair. Whatever the habits and relationships of Saurodectes, there can be little doubt there must have been hordes of parasites making a living off of dinosaurs that we have yet to learn about.

References

Dalgleish RC, Palma RL, Price RD, Smith VS (2006) Fossil lice (Phthiraptera) reconsidered. Systematic Entomology 31: 648-651.

Grimaldi D, Engel MS (2005) The evolution of Insects. Cambridge University Press.

Modesto SP, Damiani R, Neveling J, Yates AM (2004) Saurodektes gen. nov., a new generic name for the owenettid parareptile Saurodectes Modesto et al., 2003. Journal of Vertebrate Palaeontology 24: 970.

Rasnitsyn AP, Zherikhin VV (1999) First fossil chewing louse from the Lower Cretaceous of Baissa, Transbaikalia (Insecta,Pediculida ¼ Phthiriaptera, Saurodectidae fam. n.). Russian Entomological Journal 8: 253–255.

Puzzle Time: What's the connection?

2008-09-08T02:26:00.001-07:00

Yes, see if you can guess the connection between these two fossils.

The Drakensburg Lavas and the First Great Dinosaur Dying

2008-09-05T05:46:00.000-07:00

What you are looking at is a thick pile of basalt, that was extruded onto the Earth’s surface some 183 million years ago, during the latter part of the Pliensbachian stage (or at the Pliensbachian-Toarcian boundary, depending on whose timescale you follow) of the Early Jurassic. They are part of a 2 km thick sheet that is centred on the mountainous nation of Lesotho in Southern Africa. They take their name, the Drakensburg Group, from the Drakensburg Range, a ragged row of peaks said to resemble the back of a dragon that runs along the border of Lesotho and the South African province of Kwazulu-Natal. This large pile of basalt is an erosional remnant of a truly enormous volcanic province. Other parts of what was once a continous sheet of lava extend north to Zimbabwe, Botswana and Zambia, and westward into Namibia. What is even more jaw dropping is that if Gondwana is reassembled, then these southern African lavas (generally called the Karoo flood basalts) are just part of one enormous province that extends into the Southern tip of South America (the Chon Aike Province) and across Antarctica (the Ferrar Province) and into southern Australia. Taken together the total volume of magma that was either extruded onto the surface, or emplaced as intrusions below it, would come to more than two and a half million cubic kilometres (Wignall 2001). This volume actually exceeds the estimated original volume of the famous Deccan Traps of India, which were extruded at the end of the Cretaceous (when most dinosaur lineages famously kicked the bucket). Given that these vast volcanic outpourings seem to be linked with mass extinction events with disturbing regularity it seems odd that the truly enormous Karoo-Ferrar province is not linked to a big extinction event – or is it?
An extinction event amongst marine molluscs (yay! see molluscs have much to teach us!) in the late Pliensbachian has been recognised in Europe and South America and this has been tied to the Karoo-Ferrar eruptions (Hallam 1961, Aberhan and Fürsich 1996). But the general consensus is that this was a weak mass extinction, well below the level of the ‘big five’ mass extinctions.
But how sure can we be? One thing that is clear to dinosaur aficionados is that the early Middle Jurassic has an abysmal record of terrestrial faunas and this may well be masking the effects of a terrestrial mass extinction. Indeed the first stage of the Middle Jurassic Epoch, the Aalenian, is the only Mesozoic stage that does not have its own valid, diagnostic dinosaur taxon (or at least it didn’t a few years ago, maybe there is one now). Another thing that the dinosaur record shows is that prior to the middle Jurassic, dinosaur faunas were rather uniform the world over with a community structure dominated by basal sauropodomorphs (usually a massospondylid) with small coelophysid and larger dilophosaurids representing the theropod contingent and much rarer small basal ornithischians. This type of fauna can be found in Southern Africa (Elliot, Clarens and Forest Sandstone Formations), North America (Kayenta, Navajo and Portland Formations), Antarctica (Hanson Formation) and China (Lower Lufeng Formation). It is interesting that the two dominant components of this faunal association, the basal sauropodomorphs and the coelophysids are basically holdovers from the Triassic. However once the record picks up again higher up in the middle Jurassic things have changed a great deal. Gone are the coelophysoids and basal sauropodomorphs*. In their place we find ceratosaurs and tetanurans filling the large predator niches while eusauropods and eurypods (that is ankylosaurs and stegosaurs) occupy the large herbivore niches. This combination of taxa remained dominant around the world to the end of the Jurassic. So was this turnover a gradual affair? Maybe not, and I have suggested that there was actually a terrestrial mass extinction event that cleared away the coelophysoids and basal sauropodomorphs in my so far unpublished chapter in the upcoming Complete Dinosaur II. If so, it would seem very likely that this event was the same one that killed those poor little clams in the late Pliensbachian. In other words the Drakensburg and associated lavas really were significant for dinosaur evolution. Perhaps without them we may never have got such majestic beasts as Apatosaurus and Brachiosaurus. Quite independently Ronan Allain and Najat Aquesbi came to the same conclusion in their monograph on Tazoudasaurus, which I featured here. Ronan and myself must think alike for this isn’t the first time we’ve come up with the same idea more or less simultaneously. Earlier we both published the connection between the dating of the Karoo-Ferrar volcanics and the age of Vulcanodon at more or less the same time (Allain et al.2004, Yates et al. 2004).
Nevertheless there exists an alternative explanation. A team of French geologists led by Fred Jourdan have suggested that the late Pliensbachian extinction event was really mild because the Karoo-Ferrar basalts were extruded over an extended 8 million year period (Jourdan et al. 2005). Other continental flood basalt provinces show a pattern where 90% or more of their volume is extruded in a brief spell of less than 600 000 years. Jourdan et al. clearly demonstrated that the lavas to the north of South Africa were extruded over a period extending from 182 to 177 million years ago. Does this spell the end of the late Pliensbachian dinosaur extinction hypothesis? Perhaps but I’m not ready to discard this idea just yet. Note that the long duration of eruptions is restricted to regions north of South Africa. The Drakensburg (an erosiaonal remnant of a truly vast area shown by the intrusions that riddle the rest of the Karoo Basin) still yields a tight cluster of dates, while palaeomag indicates the whole pile experienced just one magnetic reversal (Duncan et al. 1997). What we need is a comprehensive sampling of the Antarctic, South American and Australian lavas to see whether they also extruded rapidly at the same time the Drakensburg lavas were extruded.

*There is one recorded Middle Jurassic basal sauropodomorph, Yunnanosaurus youngi, but I would like to see a better stratigraphic control on its age.

references

Aberhan M, Fürsich FT (1997). Diversity analysis of Lower Jurassic bivalves of the Andean Basin and the Pliensbachian-Toarcian mass extinction. Lethaia 29: 181-195

Allain R,Aquesbi N, Dejax J, Meyer CA, Monbaron M, Montenat C, Rechir P, Rochdy M, Russell DA and Taquet P (2004). A basal sauropod dinosaur from the Early Jurassic of Morocco. Comptes Rendus Palevol 3(3):199-208

Duncan RA, Hooper PR, Rehacek J, Marsh JS, Duncan AR (1997) The timing and duration of the Karoo igneous event, southern Gondwana. Journal of Geophysical Research 102 (B8): 18127-18138.

Hallam A (1961). Cyclothems, transgressions and faunal change in the Lias of North West Europe, Transactions of the Edinburgh Geological Society 18: 132–174.

Jourdan F, Féraud G, Bertrand H, Kampunzu AB, Tshoso G, Watkeys MK, Le Gall B (2005). The Karoo Large Igneous Province: brevity, origin and relation with mass extinction questioned by new 40Ar/39Ar age data. Geology 33: 745-748.

Wignall PB (2001) Large Igneous provinces and mass extinctions. Earth Science Reviews 53: 1-33.

Yates AM, Hancox PJ, Rubidge BS (2004). First record of a sauropod dinosaur from the upper Elliot Formation (Early Jurassic) of South Africa. South African Journal of Science 100: 504-506.

Jumping the gun: Similicaudipteryx

2008-08-28T00:31:00.000-07:00

Hagfish from www.itsnature.org

Hi folks, Yes its been quiet here on Dracovenator. School is back on, and I have a hectic 16 hours of teaching a week which coupled with a newborn in the house is leaving me kind of exhausted. In anycase I'm going to give voice to a few thoughts that flashed through my mind when I read the abstract for the latest dinosaur taxon to be named from the Jehol Group of Liaoning. I haven't seen the paper yet, someone want to forward the pdf?, So this should all be read as speculative thoughts and nothing more. Firstly I'm sure you are are wondering why the hell I've put up a picture of a hagfish, of all things, to illustrate a post about a dinosaur, well read on....
Similicaudipteryx yixianensis He et al. 2008 is described as a caudipterygiid oviraptorosaur in the latest Vertebrata Palasiatica. For those who may need reminding, Caudipteryx was one of the first non-avian theropods discovered with a plumage of undeniable pennaceous feathers. As one could have expected the 'BAND' didn't take to kindly to the idea of fully plumed non-avian theropod dinosaur and they fairly quickly responded with claims that Caudipteryx was actually a true bird that had become secondarily flightless and ground-dwelling. Indeed there is something terribly birdy about the incredibly stump-tailed Caudipteryx and its wing-like hand with a highly reduced third digit.

A very nice model skeleton of Caudipteryx. From www.dinocasts.com

These observations have occurred to many and even Stephen Gould wrote an essay about how blurry the bird-dino distinction had become and in this case he thought us dino palaeontologists had got it wrong. In anycase it didn't take long for people to see that Caudipteryx shared much with the mid to late Cretaceous Oviraptorosaurs. It has always been puzzling how many bird-like features Oviraptorosaurs display that are not present in the Deinonychosauria which is the currently accepted sister group of birds. These have been largely thought of as convergences because comprehensive cladistic analyses routinely place them outside the clade of Deinonychosauria + Birds. Why is this? Well for all their birdiness oviraptorosaurs have a suite of plesiomorphies including (but not limited to) a straight(versus bowed) metacarpal three , a deep ilium with a post-acetabular process that exceeds in length the pre-acetabular process, and a forwardly directed pubis with an anteriorly and posteriorly expanded boot. Now along comes Similicaudipteryx and adds a couple more bird-like features that are not seen in deinonychosaurs. One is the presence of deep hypapophyses on the anterior dorsal vertebrae and a pygostyle on the end of the tail. The latter had been previously reported in the oviraptorosaur Nomingia but had been dissmissed as convergence since other oviraptorosaurs apparently didn't have one. Similicaudipteryx raises the spectre that pygostyles may have been primitive for oviraptorosaurs and lost in later taxa (or simply not present because the material was not mature enough in the case of Caudipteryx). One more little observation before we can finally get to slime-hags: The undoubted volant pygostylian bird, Sapeornis, also from Liaoning, has a remarkably caudipterygiid-like skull as noted by Stephen Czerkas when he briefly described a specimen (under the name Omnivoropteryx).
Now to hagfish. Although the dust (slime?) hasn't settled on the controversy over their systematic position, it seems that the evidence for cyclostome monophyly (that is lampreys + hagfish) is growing. Now that is deeply uncomfortable to those used to working with morphology, since everything about hagfish seems to shout that they are basal to lampreys + jawed vertebrates. For instance they lack extrinsic eye muscles, innervation of the heart, vertebrae of any sort and muscles in the caudal fin. Nonetheless it looks like hagfish really are an example of pervasive, wholesale reversion to a more primitive condition. There are other less extreme examples of this phenomenon. For instance gavials are now firmly placed as the sister-group to tomistomines (false gavials) within Crocodylidae (based on combined, morphological and molecular analyses, including fossils) they have a suite of plesiomorphies throughout the skeleton that initially confounded morphological cladistic analyses by place gavials at the base of modern Crocodylia.

Wholesale taxic atavism in gavials. A graphic representation of morphological characters that place gavials on a more basal branch of crocodylian phylogeny. From Gatesy et al. 2003.

Gatesy et al. 2003 called this pervasive reversal 'wholesale taxic atavism'. Note that it does not appear to be the result of sustained selection for any particular ecophenotype. False gavials are also longirostrine fish-eaters but lack the wholesale atavism seen in gavials. This to my mind is a very interesting and understudied aspect of evolution.
Whatever its cause I'd like to suggest that Oviraptorosauria might end up being yet another example. If this is so I will predict that as we get a better fossil record of maniraptorans from the latest Jurassic and the Earliest Cretaceous we will find earlier and earlier oviraptorosaurs that get more and more like pygostylians. Maybe we will find a volant or recently ex-volant sapeornithid-caudipterygiid intermediate. Of course I could just be jumping the gun....

references

Gatesy J, Amato G, Norell M, DeSalle R and Hayashi C (2003) Combined Support for Wholesale Taxic Atavism in Gavialine Crocodylians. Systematic Biology, 52(3): 403 — 422

He T, Wang X-L, and Zhou Z-H (2008). A new genus and species of
caudipterid dinosaur from the Lower Cretaceous Jiufotang Formation of
western Liaoning, China. Vertebrata PalAsiatica 46(3):178-189.

Email glitch

2008-08-20T07:33:00.000-07:00

Hi to all colleagues who read this. It seems that the last weeks worth of emails that I sent from my wits account have failed to be mailed and I didn't notice. I've only just started sorting through the blizzard of messages that have swollen my inbox since Anwen was born. I dislike using my university email account for several reasons (limited space, strange inability to download most attachments, excessive spam, can only be accessed by Outlook on the Web) and much prefer to use my gmail account. If you recently sent me a reprint request on my wits account please resent your request to yatesam at the site I just mentioned above.

What was it?

2008-08-20T02:41:00.000-07:00

Wouldn't you know it?, I went to take a photo of the now-prepared mystery skull, and the thing is away on exhibition, arrgh. Nonetheless I do have a snout photo of the skull lurking in my research folder, which should make its identity rather obvious.

Yes, I'm afraid it was nothing so unusual. Just another Massospondylus skull. Nonetheless it was one I collected so I'm quite proud of it. It also came from quite a beautiful site from the Clarens Formation making it one the youngest known specimens.

Beatrix Farm in the Free State, where the skull was found.

Recently I've tallied up the number of Massospondylus skulls known (not including the Kayenta and South American specimens which, although related, are something else). There are 14 more-or-less complete skulls that I know of (if you include the two embryonic skulls, and 1 unprepared skull). Now I'm sure that there are more Psittacosaurus skulls floating around but they are divided between a host of species. Currently all these Massospondylus skulls are classified as one species, M. carinatus. Could this be the most numerous dinosaur species in terms of whole skulls?

Umbilia gazing

2008-08-18T00:04:00.000-07:00

I'll do the big reveal on the puzzle fossil tomorrow. For now I want do something I've wanted to do since I started this blog. Post on Cenozoic molluscs. Please stick around they are fascinating - and beautiful as well.
The genus Umbilia is an endemic Australian genus of cypraeid (cowry shell).
Umbilia eximia from the Miocene of Victoria and South Australia.

Cowries are marine gastropods distantly related to periwinkles (littorinids). They are generally predators on sessile invertebrates and have a distinctive shell characterised by determinate growth. As maturity approaches the outer lip reflexes, closing the aperture to a narrow slit and causing the cessation of growth. Umbilia take their name from their countersunk spires, that look like a little belly-buttons. Other features of the genus include large size, the anterior and posterior canals produced into well developed ‘beaks’ (rostra) and a poorly developed to non-existent fossula. To those not steeped in the arcana of cypraeid anatomy, the fossula is a broadened, scooped-out area on the inner wall of the aperture (the columella) at its anterior end. The diagram below should help a little.

A typical cowry shell (Trona stercoraria)showing the major parts of the shell.

In terms of life-history, Umbilia is unusual amongst cypraeids in having direct development. That is to say that they forgo the usual planktonic larval stage, instead hatching directly into benthic crawling snails. This of course severely limits dispersal ability, and may be a reason why the genus has not been able to spread beyond the continental shelf of Australia. Members of this genus have produced a number of remarkable morphologies that are very unusual amongst cowries (a terribly conservative group on the whole) although the extant species are rather boring compared to those of the past. First lets survey this diversity.

The species of Umbilia
Umbilia makes its first appearance in the fossil record in the Late Oligocene of Victoria in south-eastern Australia, specifically at one location, the Bird-Rock Cliffs of Jan Juc Beach (right next door to the famous Bell’s Beach). Two quite different species are found here, indicating that the genus has a deeper, hidden history. Umbilia prosila is one of the Bird Rock species and is the smallest member of the genus, only reaching 39 mm long, with a globular shell and weakly produced rostra.
Umbilia prosila, this and all other specimen photos are from Darragh 2002.

Indeed U. prosila is one of the plainest, simplest members of the genus. Although U. prosila may not display any of the trademark weirdness of the genus, its contemporary U. platyryncha certainly does. At 95 mm is a medium-sized species with its anterior rostrum produced out into a broad, flat spatula-like process. Posteriorly some specimens have no rostrum at all, just a pair of heavy calluses on each side of the posterior canal, while others show the the weakest signs of posterior projection. The aperture bears only sparse, weak denticulations.
Umbilia platyrhyncha

The early Miocene contains but one named species, U. angustior, which is more widespread than its predecessors, being found at a number of localities in Victoria and across Bass Strait in Tasmania as well. It is clearly related to U. platyrhyncha but differs in smaller size, a narrower and less flattened anterior rostrum and a weakly developed posterior rostrum. Some specimens also show a vague pair of tubercles on the dorsal surface of the anterior rostrum.
Umbilia angustior

The species may have extended at least as far west as the Murray Basin of South Australia but the appropriate aged rocks (the Mannum Formation) only contain poorly preserved cypraeid moulds and casts that are presently inadequate for diagnosis. This is a common problem for the Cenozoic marine sediments of South Australia. It seems that here the section is dominated by porous bioclastic calcarenites that have allowed groundwater to flush away the original aragonite that made the shells of cowries and indeed most other molluscs. My pet hypothesis is that this is due to the drier climate of South Australia during the Cenozoic compared to Victoria, so that there were far fewer creeks and rivers dumping terrigenous silt and mud into the sea that would eventually settle out and protect the aragonite shells from the ravages of groundwater.
Like many other molluscan clades, Umbilia radiates drammatically in both diversity and disparity in the middle Miocene. This is when the shallow epicontental seas of southern Australia reached their maximum extent. Five species have been recorded from the middle Miocene and a sixth (described by yours truly) is in press. Commonest of these was U. eximia.
Umbilia eximia

It is a moderately large species, similar in size to the extant U. hesitata. It has a shorter anterior rostrum than either U. platyrhyncha and U. angustior but has a well-developed posterior rostrum that is usually bent toward the body wall. The anterior rostrum bears a strong pair of knob-like tubercles on its dorsal surface. These may indicate that the species is related to U. angustior or may even be a direct descendant of it. Another feature of U. eximia is that it often displays is a set of small basal flanges on each side of the rostra. U. eximia has been found in numerous localities across Victoria and into South Australia. It is a somewhat variable species (perhaps just a function of its larger sample size) and a host of synonyms have been named in the past (U. mccoyi, U. frankstonensis, U. sphaerodoma, U. brevis, U. montismarthae). Thomas Darragh (2002) has examined the holotypes of all of these and found that they differ only slightly (by no more than the normal variation seen in a single sample from a rich site), if at all from the holotype of U. eximia. To me the most intriguing feature of U. eximia is the denticulation of the inner lip. Unlike earlier species which have rather simple weak denticulations along the margins of the aperture, the columellar denticulations become strong, close-set ridges with rectangular cross-sections that extend across at least half the width of the base. The reason that this feature is interesting that another cypraeid genus, Zoila, evolved a sympatric species (Zoila platypyga) that displays the same morphology. Earlier species of both genera have normal to weak dentitions, as do all species of both genera after the middle Miocene. Why? The best hypothesis I can think of is that the middle Miocene of south-eastern Australia was home to a predator that specialised on cypraeids in the 90-100 mm size range (there are both larger and smaller sympatric cypraeids that do not show this modified dentition) and that these highly elongate ridges could have been an adaption to stop propagation of cracks when the shell was placed under stress by the predator trying to break in. What was this predator? I don’t know but some kind of teleost fish or starfish seems to be likely candidate (neither have left a good fossil record in the Miocene of south-eastern Australia). Whatever it was it either went extinct or switched prey and/or tactics by the end of the middle Miocene and the elongated columellar teeth disappeared from both Umbilia and Zoila. More to come later....

References

Darragh, TA (2002) A revision of the Australian genus Umbilia (Gastropoda: Cypraeidae). Memoirs of the Museum of Victoria 59: 355-392.

Picture of the day: What is it?

2008-08-15T00:40:00.000-07:00

Given the great popularity of Darren Naish's guessing games and my complete immersion in paper writing right now, I'm going to do likewise. So here is a field photo from my archives. The specimen is now prepared. What do you think the fossil is?

A paper you may have missed

2008-08-08T00:59:00.000-07:00

Images courtesy of Fernando Abdala

Today I’m showcasing a little paper on some very intriguing little teeth (shown above) from the Triassic of South Africa that appeared last year (Abdala et al. 2007). It didn’t make much of an impact partly because of its location (the local ‘South African Journal of Science’) and perhaps also because no firm conclusions could be reached. Nevertheless it deserves comment because whatever the teeth turn out to belong to they are significant, indeed they have the potential to be extremely significant.
The teeth in question were recognised when Helke Mocke, then an honours student at the BPI who was being supervised by Fernando Abdala, was attempting to find isolated cheek teeth of Bauria, a therocephalian therapsid with some striking convergences with mammals. Helke was attempting to test the hypothesis that Bauria was an herbivore by looking for dental microwear on the cheek teeth. Most of the Bauria in our collections either have the lower jaws tightly clamped against the upper jaws making it impossible to see the chewing surfaces of the teeth, or had the teeth mechanically prepared out of hard matrix with airscribes and pins, potentially adding a whole new set of scratches and microwear that had nothing to do with the diet of the animal. Bauria comes from the middle part of the Burgersdorp Formation of the Karoo Basin. This part of the formation is thought to be latest Early Triassic in age and is also the source of such well known extinct animals as Erythrosuchus, Cynognathus and Kannemeyeria. It is here that I play a very minor role in the story. I suggested to Helke that she might find good Bauria teeth in the older parts of the Burgersdorp Formation. The older parts (known informally as the ‘A zone’) are generally rich in aquatic or subaquatic taxa such as lungfish, hybodontid sharks and temnospondyl amphibians but a rich channel lag deposit found by palaeontologist/geologist John Hancox is crammed with all sorts of small vertebrate fossils, including some terrestrial creatures. Amongst them were teeth that had been identified as bauriid. These could be isolated by simple surface picking at the site, or screen washing in the lab. So Helke proceeded to look at the A zone bauriid teeth with a microscope. As it turned out this was the first time anyone had given these teeth anything more than a cursory glance. Surprisingly they weren’t bauriid teeth at all. Even more surprisingly the crowns of these teeth resembled nothing more than those of early mammals called haramiyidans. Compare the A zone teeth featured above with those of a haramiyidan below)

Haramiyavia, from Jenkins et al. 1997.

Haramiyidans themselves are an enigmatic group known only from teeth and incomplete jaws (apparently there are some postcranials of Haramiyavia but these are rather uninformative). Their cheek teeth bear double rows of small cusps, similar to those of multituberculates, which they are often grouped together with in the clade Allotheria. Multituberculates have a derived therian-like shoulder girdle, indicating that they share a more recent common ancestor with them than monotremes or other major Mesozoic mammal groups like eutriconodonts, docodonts and morganucodonts. The earliest haramiyidans are from the late Norian Stage of the Late Triassic. If they are truly early relatives of the multis then they would push back the origin of crown group mammals, and even more significantly advanced theriimorph mammals, to a time 45 million years or more before the next oldest appearance of this clade in the fossil record. If the A zone teeth are also regarded as allotherian then we have the appearance of theriimorph mammals before the appearance of probainognathians, at a time when only the earliest eucynodonts had just made their appearance. Clearly this is strongly at odds with the known fossil record. At this point I think there are three main hypotheses that can explain these teeth. I order them here from what is in my opinion the most likely to the least likely. 1) The A zone teeth are convergently similar to haramiyidans and do not belong to a mammal at all. 2) The A zone teeth are early haramiyidans but haramiyidans are themselves an early branch of cynodonts and are not mammals. 3) The A zone teeth are haramiyidans and haramiyidans are allotherian mammals. This last hypothesis implies a huge stratigraphic debt, with ghost lineages for chiniquodonts, probainoganthids, trithelodonts, tritylodonts, morganucodonts, Sinoconodon, docodonts, Hadrocodium, Kuehneotherium, australosphenidians and stem trechnotherians all extending back to the Early Triassic.
Multicusped rasping teeth have evolved multiple times in synapsid evolution with tritylodontids, multituberculates and ektopodontids all being independant examples (I am sure there are more). The A zone teeth are single rooted (like basal cynodonts but unlike almost all advanced cynodonts including mammals and haramiyidans) which supports hypothesis 1.
If they are only convergently mammal-like then what are they? We can't say now but I like the idea that maybe they are derived bauriids afterall. The answer will be forthcoming from the next field trip, I hope.
Oh, we still don't know what Bauria ate.

References

Abdala F, Mocke H, Hancox PJ (2007) Lower Triassic postcanine teeth with allotherian-like crowns. South African Journal of Science 103: 245-247.

Jenkins FA Jr, Gatesy SM, Shubin N, Amaral WW (1997) Haramiyids and Triassic mammalian evolution. Nature 385: 715-718.

picture of the day: Dicraeosaurus

2008-08-04T00:57:00.000-07:00

Once again no time for a decent post - I'm going into hospital tomorrow for a minor procedure and will be off for a few days so the lack of activity will continue I'm afraid. Anyway this is a rough sketch from my notebook that I drew in the old dinosaur gallery of the Humboldt Museum in Berlin. Dave Unwin had given us (myself and Max Langer) after hours access to the gallery. I should have been furiously taking this once off oportunity to note and photograph as much as possible but I rapidly became exhausted (it had been a very hectic study trip) so after a short look at the Elaphrosaurus mount. I plonked myself in front of the Dicraeosaurus skeleton and drew this. I'm very happy with the way the head and neck turned out (note that the nostrils are in the pre-Witmer position).

Picture of the day: Golden Gate

2008-07-30T23:48:00.000-07:00

I have no time for a lengthy post, I'm in the midst of teaching three honours modules and trying to catch up on a backlog of research papers I need to write. I got a big one away just last week...
Anyway this picture shows Golden Gate National Park at Rooidrai (Red Corner) where James Kitching found the Massospondylus embryos that featured in Science a few years back. The large sandstone bluffs are aeolian deposits belonging to the Clarens Formation, while the red friable rocks below are the fluvial mudstones and sandstones of the Elliot Formation. The embryos were found in the spoil heap created by blasting for the road. You can see the heap to the right of the truck ('bakkie'pronounced 'bucky' in South African) disappearing off down the gully.

Monographs aint dead

2008-07-28T23:58:00.000-07:00

A common lament amongst the vertebrate palaeontology community is the trend toward quick, brief publications in high-impact journals with long delayed to non-existant followup with detailed descriptions. The problem is a symptom of today’s ‘publish or perish’ academic climate where the cost of spending a lot of time producing a monograph that will inevitably appear in a low impact journal can actually harm an early career. I am guilty of adding to the problem myself. Five years after my publication of Antetonitrus in the Proceedings of the Royal Society the descriptive osteology is still in preparation (though not because I don’t wish to produce it, it is just that so many other projects have pushed their way to the front of my to do list). Fortunately more organised and focused researchers have not forgotten the value of a thorough descriptive osteology for the good of the science, if not the individual. One of these crossed my desk last week. “Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco” does exactly what it says on the cover and how sorely was this needed! Tazoudasaurus is a relatively newly named Moroccan sauropod from the Early Jurassic. It is significant because it is rather completely represented non-eusauropod. For those only cursorially interested in dinosaurs eusauropods are the 'classic' sauopods with enormous bodies, long necks, tiny heads with large retracted nostrils, unique tubular, fingerless hands atop elephantine limbs and lightweight vertebrae constructed from thin laminae. In all the construction of the eusauropod 'bauplan' is one of the great transformations in dinosaur, if not vertebrate, evolution equal in my mind to the evolution of birds. Sadly our understanding of this evolution has been severely hampered by the extremely fragmented nature of pre-eusauropod sauropods. The usual standard basal taxon is Vulcanodon which is hopelessly fragmentary as you can see in the diagram below. There is enough of Vulcanodon to show that it is clearly outside Eusauropoda but it tells us nothing about the evolution of dorsal vertebrae (which must really bother these guys), hands or the skull. Help is now at hand: Tazoudasaurus is clearly a close relative of Vulcanodon (the monograph adds new derived character states which shores up the monophyly of Vulcanodontidae) and it preserves some skull bones along with good neck and dorsal vertebrae and a complete articulated hand.
It is apparent that vulcanodontids are actually quite close to Eusauropoda and are distinctly more advanced than the fragmentary rabble of basal sauropods that has been steadily accreting to the base of Sauropoda in recent years (e.g. dinosaurs like Antetonitrus, Gongxianosaurus and Isanosaurus). For instance the dorsal vertebrae have transversely expanded laminar neural spines, unlike the transversely flattened, plate-like affairs seen in the aforementioned trio. The hand is really cool. The palm is not wrapped into the semitubular arrangement seen in eusauropods, and the fifth metacarpal is still quite a bit shorter than the others (as in prosauropods) but the fingers are reduced right down to mere clawless stumps.
Given the high number of synapomorphies linking vulcanodontids and eusauropods over the more 'prosauropody' taxa like Antetonitrus, Allain and Aquesbi go ahead and erect a new higher level taxon: Gravisauria ('the heavy lizards'), an action I support.
The authors also discuss faunal turnover at the end of the Early Jurassic but I want to save that for another post, not least because I had come to identical conclusions and even have the idea in press (where it will probably linger for another year). If you like sauropods get a hold of this paper (no I do not have a pdf).

Allain, R., Aquesbi, N. (2008). Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco. Geodiversitas, 30(2), 345-424.

Dinosaur supertree- Mark II

2008-07-23T00:09:00.000-07:00

Back in the day when I was a postdoc at the University of Bristol I was involved in a project to build the first supertree for non-avian dinosaurs (Pisani et al. 2002). Now our initial efforts have been thoroughly superseded by a new supertree created by a new team, also from Bristol, headed up by Graeme Lloyd. What is a supertree? Basically its a very large phylogenetic tree stitched together from smaller trees made from standard cladistic analyses of a feasible size (known as source trees). This might, at first, sound like a trivial operation but when you have partially overlapping sets of taxa in the source trees it quickly becomes a calculatory nightmare to produce a rigorous consensus of the source trees. About the only feasible solution available then (and probably still now) was Matrix Representation using Parsimony, or MRP for short. In this technique each node in each tree was treated as a character and all of the ingroup members of that node are coded as '1' whereas all outgroup members are coded as '0'. Taxa that don't appear in that particular source tree are given a '?'. In effect the 'winning' signal from each analysis has all competing signals stripped away and then is combined with all the other 'winning' signals from the other source trees. A large matrix is thus compiled and can be analysed using standard parsimony-based techniques. Some of the early practitioners of supertrees got quite carried away with this and thought that by combining all these small sub-signals together a new signal, perhaps more closely approximating the truth than any other, was created. I lampooned this point of view at SVP with the slide: "Supertrees - a marvelous new way of generating new, more inclusive phylogenies without all that tedious mucking about with actual specimens" (Hat tip to the comic genius of Douglas Adams). No, in my view, supertrees should only be used as a consensus technique to form baseline phylogenies for other studies. It is good to see that that is how the supertree is used in the Lloyd et al. paper. So what did they use their supertree for?
The supertree was used to look at the evolution of dinosaur diversity through time. Unsuprisingly they found that raw diversity was strongly affected by sampling bias. Crudely put there are a lot of Late Cretaceous Dinosaurs because there are a lot of late Cretaceous rocks and a lot of man-hours have been spent collecting from them. Perhaps a little more surprising is the find that after a initial burst of adaptive radiation, dinosaur diversification proceeded at a fairly steady pace throughout the Mesozoic and did not appear to change during the KTR (Cretaceous Terrestrial Revolution) where modern ecosystems were forged by the explosive radiation of flowering plants, insects and numerous other modern groups.
David Hone is one of the authors on this new effort and he gives a much more over at archosaur musings

References

Lloyd, G.T., Davis, K.E., Pisani, D., Tarver, J.E., Ruta, M., Sakamoto, M., Hone, D.W., Jennings, R., Benton, M.J. (2008). Dinosaurs and the Cretaceous Terrestrial Revolution. Proceedings of the Royal Society B: Biological Sciences, -1(-1), -1--1. DOI: 10.1098/rspb.2008.0715

Pisani D, Yates AM, Langer M, Benton MJ (2002) A genus-level supertree of the Dinosauria. Proceedings of the Royal Society B 269: 915-921

The carebear-palaeontology connection

2008-07-21T06:25:00.000-07:00

One of the little charms(?) of South African life is the stuff they put on the telly. Mostly it is absolute dreck (failed American drama pilots and embarrassing action films that even Bill Bixby wouldn't be seen dead in*) and ancient shows excavated from the fossil record of television that the rest of the world has long since forgotten. Just last week I was minding the kids at home and Melanie was watching the Carebears. I've a vague recollection of these obnoxiously saccharine-flavoured bears from my childhood but it was not a craze that ever penetrated my world back then. Anyway it seems that the aforementioned bears have a nemesis, namely one Professor Coldheart. I was struck by the resemblance between Prof. Coldheart and none-other than Richard Owen himself (maybe its just me - judge for yourselves)

By all accounts Professor Coldheart would be an excellent description of Owen. I wonder if the creator(s) of the carebears were in some way palaeo aficionados.

*yes I shamelessly lifted these words from an old favourite. I doubt ANYONE reading would be able to recognise it however.

The most primitive short-tailed bird?

2008-07-18T03:35:00.000-07:00

The latest issue of Palaeontology is choc-full of palaeo goodness. I might end up blogging quite a bit of it, then again time may elude me. For now I just want to say a few quick words about the paper by Gao Chunling et al. It describes yet another new bird from the Yixian Formation of Liaoning, China. Called Zhongornis haoae, Gao et al. bestow upon it a relatively high degree of importance because they believe it to be the sister group of all other short-tailed birds, a clade called Pygostylia. The image is from their paper (Gao et al. 2008). As the name would suggest pygostylians are characterised amongst other things by having a reduced number of tail vertebrae where the distal most ones are fused into a single element called the pygostyle. Although Zhongornis has various advanced pygostylian characters such as an elongate strut-like coracoid and a short tail (just 13 caudal vertebrae), it does not have a pygostyle. That is all 13 caudal vertebrae are unfused, separate bones. However, and this is a big however, it is clearly a juvenile specimen (based on small size, lack of fusion of wrist and manual elements and porous, grainy, bone texture). An therein lies the biggest problem with accepting Zhongornis to this privileged position. Other very juvenile early pygostylians also have unfused caudal vertebrae (e.g. ' Liaoxiornis'). Clearly like wrist fusion the formation of the pygostyle did not occur until quite late in ontogeny amongst early pygostylians. Gao et al try to side-step this problem by claiming the specimen was skeletally mature, or close to maturity because it had fledged, ie. it had grown long vaned feathers from its wings (remiges) and tail (retrices). This I think is the biggest fault with the authors' reasoning. Firstly fledging itself is a variable trait with variable timing of onset amongst modern birds (if I am not mistaken the modern mallee fowl, a kind of megapode, are hatched in a fully fledged state). Late fledging can be expected to be tied to altricial lifestyles. Altriciality is a derived trait in modern birds and should not be expected amongst the early pygostylians of the Cretaceous. Indeed the very same Liaxiornis I mentioned above is a very juvenile early pygostylian with well developed remiges. This more or less falsifies the argument of Gao et al.
So what is Zhongornis? Hard to say. It is toothless so there aren't that many contemporary taxa it could be a juvenile of (Bolouchia is a possibility). It has an unique configuration of phalanges in the third finger which could argue for its status as a valid taxon (although I would classify it as Pygostylia incertae sedis, rather than the pygostylian sister group). However I even wonder if it is possible for the digit three to be reduced as the bird matures, much in the same way that the juvenile claws of the hoatzin are lost as it matures.

GAO, C., CHIAPPE, L.M., MENG, Q., OCONNOR, J.K., WANG, X., CHENG, X., LIU, J. (2008). A NEW BASAL LINEAGE OF EARLY CRETACEOUS BIRDS FROM CHINA AND ITS IMPLICATIONS ON THE EVOLUTION OF THE AVIAN TAIL. Palaeontology, 51(4), 775-791. DOI: 10.1111/j.1475-4983.2008.00793.x

I can draw a little, or.. An Anthropocene Azhdarchid Analogue

2008-07-16T05:24:00.000-07:00

As you could well imagine, I really haven't had time to write much blog material of late. So I'm showcasing one of my drawings. Its a Southern Ground Hornbill. Seriously if you like it the original is for sale (price negotiable). The proceeds will help me and my family get to the UK next year for SVP Bristol.

Sad News

2008-07-15T23:47:00.000-07:00

Yesterday, quantative morphologist and physical anthropologist Charles 'Charlie' Lockwood died in a motorbike accident in London. The story has been covered elsewhere but I wanted to add my voice to those sending their condolences to the Lockwood family. This is especially sad news for people from Wits for Charlie was due to take up his appointment as the first director of the newly created Institute of Human Origins at Wits University here in Johannesburg. I only met Charlie on a couple occasions as he visited Wits but I found him to be an affable and dynamic young scientist. I was looking forward to see the IHE (which has close ties to the BPI where I work)grow under Charlie's leadership. Alas it was not to be.

Sleeping Beauty

2008-07-11T03:22:00.000-07:00

I couldn't resist posting a picture of Anwen.

Tracking basal sauropodomorphs

2008-07-11T02:15:00.000-07:00

This is the long-delayed third instalment of my sauropodomorph trilogy. This discussion was sparked by a recent paper published in Acta Palaeontologia Polonica (Milàn et al. 2008). Laelaps has already blogged about this paper many weeks ago, but as I said it takes me a while to get around to things.
One feature of Late Triassic (Norian – Rhaetian) and Early Jurassic faunas is the usual dominance of basal sauropodomorph dinosaurs. I say usual because it wasn’t a global hegemony. Basal sauropodomorphs are strangely absent from the Triassic of North America. There are some reported scraps and a few teeth but these are not very convincing (see Nesbitt et al. 2007). Otherwise the sole Triassic records of Sauropodomorpha from the continent are the Eosauropus tracks, which may represent true sauropods but this remains contentious. Basal sauropodomorphs are likewise absent from the admittedly meagre Early Jurassic record of Europe (Ohmdenosaurus, a vulcanodontid-grade sauropod is an exception). However all other rich deposits are chock full of basal sauropodomorphs. Take the Elliot Formation for example: here it would be no exaggeration to suggest that more than 90% of finds in the upper part (Early Jurassic) are basal sauropodomorphs, while this proportion very nearly reaches 100% in the lower part (Late Triassic) of the formation. I mention all of this was just to establish the point that basal sauropodomorphs are very common in the body fossil record. So one might expect an equally rich footprint record. Not so, the footprint record from the early phase of dinosaur history is heavily biased in favour of theropods, which are the rarest of body fossils. All I can think of to explain this is that theropods, especially the coelophysoid-grade theropods from the Late Triassic and Early Jurassic loved to patrol lake margins and river side point bars where their tracks were more likely to be preserved.
The scarcity of non-theropod footprints is made all the more vexing by the inability of ichnologists to decide which of the remainder, if any at all, were made by basal sauropodomorphs. Perhaps the most commonly cited example is a single quadrupedal trackway in the Early Jurassic aeolian sandstone of the Navajo Formation. Called Navahopus falcipollex, interpretative drawings show a large four-toed hindfoot and a smaller, pronated (turned so the palm faces backward) forefoot with a large medially directed thumb claw (Baird 1980). The trackway was made in loose sand, as the animal travelled up a sand-dune, consequently details are not well recorded. Indeed many would suggest that the original reconstruction of the manus print goes too far. I failed to see an obvious thumb-claw print when I had a chance to look at a cast of the trackway. Indeed it seemed to me that partial infilling of the manus prints, where loose sand had spilled into the print from the leading (upslope) edge, had resulted in the transversely elongate, antero-posteriorly shortened manus prints. Hunt and Lucas (2006) also doubted that Navahopus was left by a sauropodomorph, noting that the supposed pollex print was not as robust as reconstructed by Baird and was rather thin and variable in its expression. Lockley and Hunt (1995) suggested that Navahopus was just a large, poorly preserved Brasilichnum (an ichnogenus believed to have been made by tritylodontid cynodonts). If Navahopus was left by a tritylodontid, then it would have had to have been a big one. That’s ok though, unusually large tritylodont body fossils are not unheard of, despite the common misconception that all synapsids in the age of the dinosaurs were small rat to shrew-sized creatures. Pictured here is a fox-sized tritylodont from the Early Jurassic Clarens formation of South Africa. It looks crappy because it is a cast made from a natural mould of the skeleton in coarse sandstone.
So if Navahopus isn’t a basal sauropodomorph track then what is? There are two main contenders: Tetrasauropus and Otozoum. I have little doubt that the Early Jurassic Otozoum prints fit the bill nicely. Otozoum are medium to large four toed tracks of a biped. One track records a moment when an individual got down on all fours but didn’t take any steps until it got back up onto its hindlegs. The diagram on the right shows an Otozoum footprint and the one known track way with hand prints (shown in grey). Both are redrawn from Rainforth (2003).
The digital proportions and apparent phalangeal formula of the feet (based on the admittedly dodgy method of using toe pads) match those of basal sauropodomorphs. Emily Rainforth’s 2003 paper sets out the evidence nicely and a convincing case is made. What really tickles me however is that the Otozoum matches very nicely the predictions made by Matt Bonnan and Phil Senter (2007) based on the skeletal anatomy of the shoulder girdle and forelimb of plateosaurian-grade basal sauropodomorphs like Plateosaurus and Massospondylus. They found that in these dinosaurs had very limited degrees of humeral abduction (that is sticking their forearms out laterally) and could not rotate their wrists either. Thus they were denied any means to bring the hand into a forward facing (pronated) position seen in the Navahopus tracks and were forced to keep their palms facing inwards, theropod style. This is exactly what is seen in the one Otozoum track where the animal briefly went down onto all fours. Some have argued that the lack of a print of a large recurved thumb-claw in this track argues against Otozoum being the track of a basal sauropodomorph. However modelling of the range of motions of the joints of the hand shows that it was perfectly possible for plateosaurian-grade sauropodomorphs to lift their large sharp thumb claw well clear of the ground when on all fours. The picture on the right is a reconstruction from Galton (1971) that shows the likely stance of the hand when it was placed on the ground.

Finally we now turn our attention to the featured paper. The Jesper Milàn and colleagues report on a new, better preserved Navahopus trackway (skipping over the theropod tracks entirely). Suprisingly (to me in any case) it more or less confirms Baird’s earlier interpretation of Navahopus. In particular the manus prints are much clearer and lo and behold there is a large medially directed thumb-claw. Sauropodomorphs are the only known four-toed tetrapods from that epoch with hyperenlarged thumb claws so I think we have to accept that Navahopus was indeed the spoor of a sauropodomorph. So what is Otozoum, and were basal sauropodomorph facultative quadrupeds after all? I think a plausible explanation is that we are dealing with two distinct kinds of basal sauropodomorph. Otozoum tracks were likely left by plateosaurian-grade basal sauropodomorphs (like Plateosaurus and Massospondylus), which probably were obligate bipeds (at least as adults). Navahopus, on the other hand was probably left by a basal sauropod, or near-sauropod sauropodomorph (like a smaller version of Antetonitrus or Melanorosaurus). These advanced near sauropods and early true sauropods do show the necessary modifications to their forelimbs, which would have allowed them to pronate their hands. Such a beast has yet to be found in the Navajo Formation but given the general paucity of vertebrate fossils in this unit I’m not unduly fussed about it. Is Navahopus unique or are there larger prints attributable to large Antetonitrus or Melanorosaurus-like creatures. Yes there are. The original Tetrasauropus unguiferus track from the Elliot Formation seems to be just such a track. It was produced by a large, quadruped with a four-toed hind foot and a smaller, pronated hand that bore a moderately large medially directed claw that made contact with the ground. Some have opined that this was left by a large crurotarsan (e.g. Rainforth 2003) largely on the grounds that it didn’t match Otozoum, which was taken to be a true basal sauropodomorph track. As I’ve suggested above it is possible that these tracks could both be sauropodomorph, and just represent different grades of basal sauropodomorph evolution.

References

Baird D (1980) A prosauropod dinosaur trackway from the Navajo Sandstone (Lower Jurassic). In: Jacobs LL, ed. Aspects of Vertebrate History. Essays in Honour of Edwin Harris Colbert. Flagstaff, Museum of Northern Arizona Press. pp. 219-230.

Bonnan MF, Senter P (2007) Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadrupeds? In: Barrett PM, Batten DJ, editors. Evolution and palaeobiology of early sauropodomorph dinosaurs, Special Papers in Palaeontology 77: 139-155.

Galton PM (1971) Manus movements of the coelurosaurian dinosaur Syntarsus and opposability of the theropod hallux. Arnoldia 5:1-8.

Hunt AP, Lucas SG (2006) The taxonomic status of Navahopus falcipollex and the ichnofauna and ichnofacies of the Navajo Lithosome (Lower Jurassic) of Western North America. New Mexico Museum of Natural History and Science Bulletin 37: 164-169.

Lockley MG, Hunt AP (1995) Dinosaur tracks and other fossil footprints of Western United States. New York, Columbia University Press. 338 pp.

Milàn J, Loope DB, Bromley RG (2008) Crouching theropod and Navahopus sauropodomorph tracks from the Early Jurassic Navajo Sandstone of USA. Acta Palaeontologia Polonica 53: 197-205.

Nesbitt SJ, Irmis RB, Parker WG (2007) A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5: 209-243.

Rainforth, EC (2003) Revision and re-evaluation of the early Jurassic dinosaurian ichnogenus Otozoum. Palaeontology 46: 803-838.

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image at top of page from wikipedia commons.

Virtual cigars for all!

2008-07-09T03:12:00.000-07:00

Remember I mentioned a medical emergency the week before last? That was our pregnancy, which was not progressing well. So bad infact that the doctors had decided that to continue it full term would have endangered both the baby and her mother. So this morning, Anwen Jordan Yates was born by C-section. Despite being just over seven weeks premature she weighed 2.5 kg and is doing well in ICU.

There can be only one ........ Diprotodon

2008-07-07T02:24:00.000-07:00

Every natural history buff that I know has a set of favourite taxa that captivates a disproportionate amount of their attention. For me there are the dinosaurs (of course), whales, beetles and Banksias amongst others, and the Diprotodontoidea. Diprotodontoids were large quadrupedal browsing marsupials from Australia. First appearing in the Oligocene, they ranged from dog-sized up to white rhino sized and were Australia’s largest herbivores up to their abrupt extinction in the late Pleistocene. Perhaps my interest in these megaherbivores arose because the first mounted skeleton of an extinct vertebrate I ever saw was a diprotodontoid. In fact it was the Diprotodon skeleton that used to stand near the entrance to the galleries of the South Australian Museum (shown on the right). Growing up in what is, after Antarctica, the most dinosaur-poor continent meant that this skeleton was as close to a dinosaur as I was going to get for quite a while. It was sufficiently weird enough for me. With its unusual retracted nose and my poor anatomical knowledge (I was only five or six when I first saw it) I mistakenly imagined the eyes fitting in the narial opening giving it a bizarre otherworldly appearance. Actually it vaguely resembles the giant South American rodents like Hydrochoerus and Josephoartigasia.

Giant Rodent (Josephoartigasia) on the left compared to Diprotodon on the right.

Diprotodon was one of the last diprotodontoids and the largest of all. Its species taxonomy has remained confused due to a flurry of poorly diagnosed species being named during the nineteenth century. Most palaeontologists have recognised a large and a small form, although the species name for these is uncertain (D. optatum is often used for the large form and D. minor is often used for the smaller). If we wish to know how many species perished during the late Pleistocene megafaunal extinctions and what their ecological and geographical distributions were we need to know how many Diprotodon there were and where and when they lived. Enter today’s featured article, a much needed, and long overdue, taxonomic review of Diprotodon by Gilbert Price (2008). Price looked at all type specimens and large collections from all major sites bearing multiple individuals (of these Bacchus Marsh, Darling Downs, Myall Creek and Lake Callabonna are most important). An analysis of adult tooth size indicates a bimodal size distribution at most localities. The exception was Bacchus Marsh where only the small morph was present. A look at the rest of the morphology showed that there was almost no other consistent difference between the two morphs save for the shape of the mandible. The smaller morph tends to have slightly shallower mandibles with a more rounded profile. This is most noticeable in the symphyseal region where the large morph develops a pronounced ‘chin’ with a steep anterior margin (even in juvenile specimens of the large morph). There certainly was other variation, particularly in the upper premolar, but this was inconsistent, with no apparent pattern even within samples from a single horizon at a single locality. Some had well developed parastyles, others not, some of them had a well developed buccal cingula, others not, some of those with parastyles had buccal cingula,while others didn’t and so on. Price concluded that the small premolar was less significant for Diprotodon feeding and so was open to more variation than is usual in other diprotodontian marsupials. The overall conclusion of this study was that since the large and small morphs co-occur at most localities, show no obvious trophic specialisations and are almost identical except for size and mandibular shape then they represent sexual dimorphs of a single widespread species. So why is only one morph represented at Bacchus Marsh? Price speculates that like some other dimorphic mammalian megaherbivores Diprotodon lived in segregated herds. The geology and taphonomy of the Bacchus Marsh site suggests that the Diprotodon (which show an unusual degree of articulation) represent a single mass death assemblage. The fossils of Lake Callabonna represent a chance to test these ideas. At this site numerous animals became mired in the floor of the lake (which obviously dried out intermittently in the Pleistocene – as opposed to its perennially dry state now). It seems that this happened several times over many thousands of years accumulating several spectacular Diprotodon fossils, including a mother preserved with a very young individual between her legs (presumably it was a pouch bound joey). Sadly the field records of the original digs are inadequate to sort out if the large and small morphs were preserved in segregated groups. Even more frustrating the pouch young was separated from its mother and we can no longer associate it with its correct adult skeleton, thus we cannot test the hypothesis that the small morphs were the females. I would say that this provides ample reason to re-open excavations at Lake Callabonna.
Price further notes that if he is correct in his interpretations then Diprotodon was spread virtually continent wide, in all sorts of habitats from woodland to semi-arid saltbush plains. In other words it was an ecological generalist. This poses a little bit of a problem for those who would deny the hand of Homo sapiens in the late Pleistocene megafaunal extinctions of Australia. Severe climatic change may well have caused loss of suitable habitat in the dry center but surely huge swaths of suitable habitat remained around the margins of the continent?
One final note. The holotype of D. optatum (the type species) has the shallow rounded mandibular symphysis of the small morph. If we eventually do decide that the large and small morphs represent two sympatric species, then D. optatum would be the valid name of the small morph (not the large morph it is commonly ascribed to) and the next available name for the large morph would be D. annextans.

References

Price GJ (2008) Taxonomy and palaeobiology of the largest-ever marsupial, Diprotodon Owen, 1838 (Diprotodontidae, Marsupalia). Zoological Journal of the Linnean Society 153: 369-397.

I'm Back: picture of the day

2008-07-04T04:42:00.000-07:00

Well that took a lot longer than expected. It appears my computer is on its last legs. The guys at the shop were unable to fix it, suggesting that the logic board was at fault and this would basically be a good time to buy a new computer. In frustration I thumped the thing and wouldn't you know it started working again, but it is prone to frequent crashes. Anyway to give all three (possibly four) of my readers something to look at while I get my workload sorted out here is an old (2000)reconstruction of mine. The quality is bad because it is a scan of a photocopy of a bromide of the original. It shows the chigutisaurid temnospondyl Siderops pulling the theropod Cryolophosaurus to its death in a frigid pool in the Early Jurassic of Antarctica (Siderops is known from similar aged sediments in Australia and South Africa so it is no big deal to put it in between in Antarctica). Next week - a bunch of posts on peer reviewed science - I hope.

An unexpected run of bad luck

2008-06-30T06:41:00.000-07:00

Hi,

This isn't the third installment of my sauropodomorph trilogy. The latter half of last week was best with all sorts of happenings including server failures, medical emergencies, power outages and topped off with my computer crashing on Friday (this is being written from a student computer in a common room at Wits). I wasn't sufficiently backed up and I've temporarily lost all my blog related files. So there is precious little for me to bring you right now, not even a nice picture. Check back soon, I hope to be up and running again by the end of the week.

A ratty old sauropodomorph caudal

2008-06-24T23:36:00.000-07:00

Meet BP/1/5339 another James Kitching find, this time a lone sauropodomorph caudal vertebra from the lower Elliot Formation (Late Triassic). It isn’t brilliantly preserved, nor has it been properly prepared yet but it is worthy of note because it is BIG. The anterior centrum face is 232 mm high and 194 mm wide, while in side view the centrum is 138 mm long. Granted this vertebra probably comes from the base of the tail where the caudal vertebrae are at their largest but it isn’t the first vertebra. There are chevron facets both fore and aft, indicating that this is at least the second caudal, or more probably the third. Compare its size to a comparable caudal (ca II) from NSMT-PV 20375, an Apatosaurus ajax (data from Upchurch et al. 2004). In this specimen the same measurements are 230, 240 and 134, respectively. I think you will agree that the two specimens are closely similar in size, although the apatosaur has transversely wider centra. This means that the Triassic of South Africa was harbouring a sauropodomorph whose tail base, at least, was similar in size to that of one of the larger Morrison neosauropods. I find that .....unexpected, to say the least. So what species does the caudal belong to? That’s another good question without a good answer. The basal sauropod Antetonitrus ingenipes is a plausible candidate. The holotype includes proximal caudals that are quite a bit smaller than BP/1/5339 but it is a juvenile. Most features of Antetonitrus are in agreement this specimen but this does not include any specific diagnostic characters. One difference that may be of significance is the strongly concave nature of the anterior centrum face of BP/1/5339, which is comparable to the procoelous caudals of advanced titanosaurs (the posterior face remains flat however). Maybe this could be a diagnostic character, or maybe it is the result of postmortem collapse. The answer is hopefully out there in the relatively unexplored exposures of the Elliot Formation.

reference

Upchurch P, Tomida Y, Barrett PM (2004) A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurasic) of Wyoming, USA. National Science Museum Monographs 26: 1-107.

Antarctosaurus - a glorious sauropodomorph

2008-06-24T00:34:00.000-07:00

So ya want sauropodomorphs do ya? Here is the first of a series of three in a mini 'sauropodofest'

The titanosaurs were quite rightly described as “the last great frontier in dinosaur phylogenetics” by Jeff Wilson. Indeed at this stage we have little idea of how the various titanosaurs are related to each other beyond a vague notion that some forms such as Andesaurus and Malawisaurus are basal to other more derived forms, of which Saltasaurus is the classic example. A big part of the problem is that although the group is diverse and many genera have been named, most are known from very incomplete remains. Skulls in particular have proved quite elusive. For a long time the best-known skull was that Antarctosaurus whichmannianus. The specimen was collected by Dr R Whichmann from the right bank of the Rio Negro, 15 km south west of General Roca, Argentina in 1912. The site was probably in the Campanian (Late Cretaceuous) Anacleto Formation. The specimen includes cranial remains and some postcranial pieces that are unquestionably that of a derived titanosaur (eg. there is a biconvex first caudal,amongst other derived titanosaurian characteristics). The skull is severely fragmented and most of the pieces are missing. Von Huene (1929) reconstructed the skull as similar to Diplodocus but with a steeper snout. This iconic reconstruction was in no small part responsible for the widespread view that titanosaurs were the derived descendants of diplodocoids. As our understanding of sauropod anatomy and evolution improved it became clear that titanosaurs were actually closer to deep-skulled sauropods (now named Macronaria) such as Camarasaurus and Brachiosaurus. Thus the Antarctosaurus skull became an anomaly. Some speculated that the skull really did belong to a diplodocoid and didn’t go with the postcranium(Jacobs et al. 1993). However there is precious little evidence of diplodocoids surviving so late in the Cretaceous. Salgado and Calvo (1997) suggested the skull had been restored incorrectly and presented a new reconstruction that presented a brachiosaurid aspect. As our knowledge of titanosaur skulls increased (thanks to skull pieces from Saltasaurus and the recognition that the so-called diplodocoids Nemegtosaurus and Quaesitosaurus were really titanosaurs) it became clear that the posterior portion of the Antarctosaurus skull was indeed that of a titanosaur. It showed several titanosaur synapomorphies such as pendant distal tips of the paroccipital processes (the braincase ‘wings’) and apparent exclusion of the squamosal from the margin of the upper temporal fenestra. However doubt about the association of the skull pieces continued. Wilson (2002) listed three derived characters of the dentary that were shared with the bizarre diplodocoid Nigersaurus (supercroc’s side-kick). It is true that jaw is remarkably diplodocoid-like, particularly with a sharp right-angled bend between the main ramus of the jaw and the toothbearing symphyseal ramus but this feature has been shown to have evolved convergently in at least one other titanosaur, Bonitasaura (Apesteguia 2004). The three characters Wilson suggested were shared specifically with Nigersaurus were 1, extension of the tooth row lateral to the main ramus of the jaw, 2, a marked increase in the number of dentary teeth and 3, restriction of the teeth to the transverse section of the jaw (= symphyseal ramus). Of these character 1 is indeed present, though only just, as you can see in the figure below.

Dentary pair of Antarctosaurus in dorsal view, created by mirroring the right dentary in photoshop. Original drawing from Huene (1929).

Character 2 is not present with three or so alveoli extending onto the main ramus, behing the symphyseal ramus, similar to the condition seen in Bonitasaura. Character 3 is not present either. There are 15 alveoli (Powell 2003), which is typical for basal macronarians, and only slightly more than in other titanosaurs (13 in Bonitasaura and Nemegtosaurus, 11 in Rapetasaurus) and a far cry from the 34 tooth columns in each dentary of Nigersaurus. Further to this the dentary lacks some diplodocoid synapomorphies that would have to have to be regarded as reversals if a special relationship with Nigersaurus is accepted. These are an increase to more than four replacement teeth per alveolus and the loss of mesial and distal carina of the tooth crowns. As in Bonitasaura there are three replacement teeth per alveolus (Apesteguia 2004) and the tooth crowns also retain mesial and distal carinae, despite their elongate diplodocoid-like shape. Elongate but carinate teeth are also present in other titanosaurs, e.g. Rinconsaurus and Ampelosaurus. Lastly the dentary displays a vertical symphyseal axis, a derived characterstic of titanosaurs. In summary there is one weak similarity with the diplodocoid, Nigersaurus, one derived characteristic of the Diplodocoidea that is convergent in some titanosaurs, the absence of two derived characters of Diplodocoidea and the presence of one derived character of titanosaurs. Following from this I think there is little reason to believe that the dentary is not that of a titanosaur. Given the scarcity of titanosaur skulls in general it seems very likely that all the cranial pieces of Antarctosaurus, which were found together at one site, belong to a single individual. Given this, I present above my own reconstruction of Antarctosaurus, using our improved knowledge of titanosaur anatomy to fill in the missing parts.

References

Apesteguia S (2004) Bonitasaura salgadoi gen. et sp. nov.: a beaked sauropod from the Late Cretaceous of Patagonia. Naturwissenschaften 91: 493-497.

Huene VF (1929) Los saurisquios y ornithisquios del Cretaceo Argentino. Annales del Museo de La Plata 3: 1-196.

Jacobs LL, Winkler DA, Downs WR, Gomani EM (1993) New material of an Early Cretaceous titanosaurid sauropod dinosaur from Malawi. Palaeontology 36: 523-534.

Powell J (2003) Revision of South American titanosaurid dinosaurs: palaeobiological, palaeobiogeographical and phylogenetic aspects. Records of the Queen Victoria Museum. 111: 1-173.

Salgado L, Calvo JO (1997) Evolution of titanosaurid sauropods. II: the cranial evidence. Ameghiniana 34: 33-48.

Wilson JA (2002) Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136: 217-276

My dark secret

2008-06-20T05:54:00.000-07:00

It is time for me to out a dark secret of mine. Dinosaurs are not my only subject of research these days. Just this year I’ve submitted papers on…….Cenozoic Mollusca. Yes fossil seashells are a passion of mine and have been so for most of my life. And why not? As an avid fossil hunter growing up in Adelaide, South Australia, Cenozoic marine invertebrates was about all that could be collected easily.
Why? The south-eastern corner of Australia was inundated with shallow seas several times during the Cenozoic (the two biggest transgressions happened in the late Eocene and the middle Miocene). The sediments left behind from these transgressions contain a rich record of the animals that lived in them. And what a fauna it was! Riotous diversity seems to be the watchword for the middle Miocene mollusc faunas. And not just high species diversity, morphological disparity seems way in excess of modern groups. Take the collectors favourite Cypraeidae, or cowrie shells as they are commonly known as an example. Although there are hundreds of modern species of these beautiful shells nearly all consist of simple ovoid shells with the smallest reaching no more than 7 mm and the largest 190 mm in length. However in the middle Miocene of south eastern Australia we find a size range that exceeds the modern global range, with the smallest adult sizes being 8 mm while the largest reaches a whopping 220 mm. Furthermore there is a species with its anterior and posterior canals produced into great upwardly curving siphons, another with a rectangular shell shape and yet another that is surrounded by a broad but thin, snowshoe-like flange. All in all I count 21 valid cypraeid species in the mid Miocene of south eastern Australia (compare this to the modern 14 or so species from the entire southern half of Australia). Similar extraordinary diversity can be seen most other molluscan families.
I’ll be returning to the lost Cenozoic seas of southern Australia several more times as my research gets published or as the mood strikes me. For now enjoy this picture of one such deposit from South Australia, the famed Mannum Formation of the River Murray cliffs. There are about 200km of almost continuous outcrop along the Murray. Its where I collected my first fossil – an irregular echinoid, Lovenia forbesi.

Lovenia forbesi