Monday, October 26, 2009

Dracovenator is moving

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!

Monday, August 24, 2009

New discoveries - Heterodontosaurus


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.

Tuesday, August 18, 2009

Spongebob is a child of snowball Earth

ResearchBlogging.org



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

Tuesday, August 4, 2009

Now is the winter of our fish content

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.

Sunday, July 5, 2009

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

ResearchBlogging.org


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.

Thursday, July 2, 2009

Another squamate post - Acontias gracilicauda




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.

Monday, June 29, 2009

Happiness is a bucket of lizards



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.

Monday, June 22, 2009

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



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.

Friday, May 29, 2009

So how did it go?

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.

Wednesday, May 27, 2009

Radio Interview

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

Monday, May 18, 2009

Organisms I Hate: Khaki Bush

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.


Tuesday, April 7, 2009

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

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.

Monday, March 30, 2009

Access Denied! When ignorance stops science

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.

Thursday, March 5, 2009

Off into the field

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.

Wednesday, February 25, 2009

stegopod!

ResearchBlogging.org

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

Monday, February 23, 2009

Egg Eating Snake


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.

Wednesday, February 18, 2009

Fossil Human Hair

ResearchBlogging.org

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

Tuesday, February 17, 2009

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


ResearchBlogging.orgI 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

Monday, February 9, 2009

Bushfire Tragedy

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.

Sunday, February 8, 2009

Another giant from the tropics: Superlucina

ResearchBlogging.org
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

Friday, February 6, 2009

Titanoboa and paleophidiothermometry


ResearchBlogging.org

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.

Tuesday, February 3, 2009

Finishing Fish Fortnight


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.

Monday, February 2, 2009

Wierdo of the Week; Protuberum cabralensis

ResearchBlogging.org
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