Gigantoraptor, Eocursor and... baby Toni

The gigantic mystery coelurosaur alluded to here in one of the ornithomimosaur articles - yes, you heard it here first - has at last been published, and it is an immense long-legged oviraptorosaur, as big as a tyrannosaur. But it is just one of three fantastic new discoveries from the world of dinosaurs that, sorry, I just had to cover...

Every now and again in the world of Mesozoic palaeontology a new discovery comes from left field and slams you in the ribs; something so surprising and counter-intuitive that it would have made a good April Fool's joke were it not actually real. Gigantoraptor Xu et al., 2007 is this sort of thing. Unlike so many new maniraptoran theropods, it is not from the Lower Cretaceous Yixian Formation, but from the Senonian Iren Dabasu Formation of Nei Mongol, and so would have been contemporaneous with troodontids and dromaeosaurids, tyrannosauroids, the therizinosauroids Erliansaurus and Neimongosaurus, the small oviraptorosaur Avimimus and the alvarezsaurid Mononykus.. not to mention ankylosaurids and hadrosaurids. The accompanying photo of a skull reconstruction gives you some idea how big Gigantoraptor was. Of its skull, only the complete lower jaw is known, but its morphology and proportions allow a reasonable guess as to the complete size and shape of the entire cranium (alas, we don't know whether this taxon was crested, like so many other oviraptorosaurs: for more on the group, there is an old post over on ver 1). The entire animal would have weighed over a ton, would have been about 8 m long, and over 3 m tall at the hips (in the skeletal reconstruction produced by Xu et al. (2007), the animal has been made to look as tall as possible by giving it an unusually straight knee joint). Its hindlimbs were highly elongate, suggesting cursoriality despite its size, and its forelimbs were, proportionally, the longest of any oviraptorosaur.

Some news articles have latched on to fact that Gigantoraptor would have been feathered. As we covered previously in the article on therizinosauroids, we just don't know whether giant maniraptorans like Gigantoraptor retained the feathery integument of their smaller relatives, and Xu et al. (2007) do actually cover this in the paper (and supplementary info). They suggest that arm and tail feathers at least may have been retained for use in display, but that maybe the feathers covering the rest of the body were reduced or lost. This remains an area where we can't do much other than speculate at the moment. I did ask Paul Maderson - an expert on feather evolution - what his thoughts were on this. He argued that, due to the fundamental reorganisation of dermal anatomy involved in feather growth, any lineage that starts out with feathers simply cannot switch back to naked skin.

I am hoping at some stage to publish an article on recently named coelurosaurs (Shanag, Sinocalliopteryx, Tsagaan, Urbacodon and so on), but haven't done this because - believe it or don't - the latest issue of Journal of Vertebrate Paleontology still has yet to arrive on these shores, and this is where Urbacodon is published. I could have kept quiet on Gigantoraptor until then, but... better to strike while the iron is hot. And anyway...

In the news on the same day is Eocursor parvus, a basal ornithischian from the Upper Triassic Lower Elliot Formation of South Africa, described by Richard Butler and colleagues (Butler et al. 2007). While its ornithischian identity means that it has, of course, received less media interest than Gigantoraptor, Eocursor is in fact a far more significant animal: it is one of the most basal known members of Ornithischia, and it reveals new information on character acquisition and morphology in the earliest members of this important group. Eocursor possesses a suite of characters unique to ornithischians, including an increased number of sacral vertebrae, the distinctive ornithischian-style pelvis, and various details of the hindlimb bones. However, it also exhibits features that are primitive for dinosaurs as a whole, most notably a relatively elongate hand with long distal phalanges, and ligament pits and condyles indicating a reasonable ability to grasp. Among ornithischians, a hand like this - more typical of saurischian dinosaurs - was previously thought unique to heterodontosaurids (discussed briefly in one of the Galve posts here). Butler et al. now suggest that it was retained by all basal ornithischians, and modified later on in the group's history [accompanying skeletal reconstruction is by Scott Hartman, and borrowed from here].

In their phylogeny, Pisanosaurus from Argentina and heterodontosaurids are more basal than Eocursor, and Eocursor itself is close to the root of Genasauria, the ornithischian clade that includes all of the familiar forms of the Jurassic and Cretaceous. Incidentally, while Eocursor adds another neat new tetrapod to the Lower Elliot Formation fauna, it was obviously greatly outnumbered by contemporaneous sauropodomorphs: in the Lower Elliot Formation these include Eucnemesaurus, Antetonitrus, Blikanasaurus, Melanorosaurus and Plateosauravus (Yates 2003). The identification of a new Late Triassic ornithischian is big news in the dinosaur world, as recent work that shown that a great many taxa originally identified as Triassic ornithischians are not, in fact, members of this group (Irmis et al. 2006).

But that's not all. A third 'significant' dinosaur paper has just appeared: Daniela Schwarz et al.'s description of 'Toni' (or, technically, SMU 0009), an outstandingly complete baby diplodocid from the Morrison Formation of the Howe Stephens Ranch in Wyoming (Schwarz et al. 2007). This little animal would have been about 70 cm tall at the shoulders and around 2 m long (image shows replica [skull and parts of neck and tail reconstructed] to scale with person). Unfused neurocentral sutures, bone surface texture and other details demonstrate that it was a juvenile. Its skull and anterior cervical vertebrae are missing, but what is preserved of the neck shows that it was proportionally short compared to that of other diplodocids. Interestingly, it was found in association with bones of an adult: a discovery that has already been alluded to in one children's book as evidence for parental care, but of course it may not mean any such thing (the general pattern we have for sauropods and many other non-avian dinosaurs is that juveniles lived in pods, essentially as separate ecological 'species' from their parents... although as usual we don't know that this goes for all species). The taxonomic identity of the specimen remains uncertain, as it combines various diplodocid characters (similar to those of Apatosaurus and Barosaurus) with unique features, such as proportionally elongate forelimbs and short neural spines on the sacral and proximal caudal vertebrae. These details might mean that the baby represents a new diplodocid taxon, or they might be features of ontogeny.

What with the also-recent appearance of the short-necked dicraeosaurid Brachytrachelopan from the Upper Jurassic of Argentina, Jerry Harris' several recent papers on Suuwassea from the Morrison Formation, and Kristian Remes' papers on the Tendaguru taxa Tornieria and Australodocus, these are clearly exciting times if you're interested in diplodocoid sauropods. In fact we routinely say the same thing about work on dinosaurs in general, so to avoid the cliché I won't say it again. But, it is a pretty exciting time if you're interested in dinosaurs.

Refs - -

Butler, R. J., Smith, R. M. H. & Norman, D. B. 2007. A primitive ornithischian dinosaur from the Late Triassic of South Africa, and the early evolution and diversification of Ornithischia. Proceedings of the Royal Society of London B doi:10.1098/rspb.2007.0367

Irmis, R. B., Parker, W. G., Nesbitt, S. J. & Liu, J. 2006. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19, 3-22.

Schwarz, D., Ikejiri, T., Breithaupt, B. H., Sander, P. M. & Klein, N. 2007. A nearly complete skeleton of an early juvenile diplodocid (Dinosauria: Sauropoda) from the Lower Morrison Formation (Late Jurassic) of north central Wyoming and its implications for early ontogeny and pneumaticity in sauropods. Historical Biology 19, 225-253.

Xu, X., Tan, Q., Wang, J., Zhao, X. & Tan, L. 2007. A gigantic bird-like dinosaur from the Late Cretaceous of China. Nature 447, 844-847.

Yates, A. M. 2003. A definite prosauropod dinosaur from the Lower Elliot Formation (Norian: Upper Triassic) of South Africa. Palaeontologica Africana 39, 63-68.