Wednesday, June 13, 2007

Giant oviraptorid and the "dawn runner"

Oviraptoroids were pretty small animals. The largest, Hagryphus, a North American form, stood about as tall an emu. That was considered huge for oviraptoroids--I mean, the next largest was Oviraptor itself at a whopping 5 feet long. Well, today's Nature issue reveals a new enoromous oviraptorosaur from the Gobi: Gigantoraptor (aptly named). The picture at left shows just hot large this monster was. The white bones indicate known material, as usual. Most of the news stories covering Gigantoraptor are focusing, ad nauseum, on whether or not it had feathers. Well who really cares? Oviraptoroids are not on the direct lineage to modern birds, and this animal certainly wasn't flying. This was an animal that could have taken on Therizinosaurus and Tarbosaurus if it felt like it. Feathers don't seem all that important. And yes, I know what you're thinking--the arms of Gigantoraptor are distinct from those of Deinocheirus and Therizinosaurus. Darnit!

And then, if you head over to the Proceedings of the Royal Society B's website, you can download Eocursor's disappointing short description. It's important because it's the most complete known ornithischian from the Late Triassic. It's skeleton is 25% complete, including a complete pelvis and leg, as well as a mandible and pieces of the pectoral girdle and arm. According to the authors, Eocursor is more derived than the heterodontosaurs and forms an outgroup to the Genasauria (Thyreophora + Cerapoda). The implications here are fairly severe: knocking the heterodontosaurs down to "most basal ornithischian" effectively knocks the idea of a monophyletic "Heterodontosauriformes" (Heterodontisauridae + Marginocephalia) down. Also, the authors assert that ornithischians as a group did not proliferate until the Early Jurassic, after the Triassic-Jurassic extinction left a bunch of herbivorous niches open.

So while saurischians got an early start, what with their carnivory (theropods) and hugeness (sauropodiforms), ornithischians were living in the shadow of the more prolific herbivorous archosaurs and therapsids like dicynodonts and aeteosaurs. It wasn't until those groups bit the big one that ornithischians were able to max out their potential during the Jurassic era.

So, two interesting finds to report today. And one of them is free online! Now, if only Nature would wise up. Looks like I've got to make a trip to the UAA library...


Verdakk said...

That's one big turkey . . . Er . . . Raptor. Kinda looks like a Weka, actually.

lantaro said...

damn! tha's a huuuuuge bitch!