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.

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

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.

stegopod!

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

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

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

A new Beipiaosaurus - beautifull plumage!

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?

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.

Predictions for 2009

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!

More sauropod vertebrae/ ceratopsian frill convergence

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 lizard biters

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.

The Drakensburg Lavas and the First Great Dinosaur Dying

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

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.

What was it?

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?

picture of the day: Dicraeosaurus

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

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

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

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

Tracking basal sauropodomorphs

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.

I'm Back: picture of the day

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.

A ratty old sauropodomorph caudal

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

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