Tuesday, February 17, 2009

Meanwhile, Back at the Sauropodomorpha...

Despite my enthusiasm lately for horned dinosaurs, I have certainly not turned a blind eye to the rest of the field of dinosaurology. Martinez & Alcober just published an incredibly important new critter, Panphagia protos, from the Ischigualasto Formation in Argentina. You might know it better as the "Valley of the Moon" where Sereno unearthed Eoraptor and Herrerasaurus back in the early 90's. That particular formation seems to be a hotbed of dinosaur evolution. While the taxonomic status of Eoraptor and Herrerasaurus swings between basal saurischians and basal theropods, the identity of little Panphagia is pretty obvious--it's the basalmost sauropodomorph known. This makes it even more primitive than Saturnalia tupiniquim, which is all kinds of awesome.

Now, take a look at that skeleton. Go ahead, give it a click. Now, pull out that old paper on Eoraptor lunensis (Sereno, et al., 1993) because the Intertubes don't have a decent skeletal of the little bugger. Anyway, compare the two. Bask in their similarities. While you're up, grab any of the following Herrerasaurus papers: Sereno & Novas, 1993; Novas, 1994; Sereno, 1993; Sereno & Novas, 1992. Because, again, Google Image Search fails. And just for the hell of it, look at this guy! Click the picture for a larger image, of course. Anyway, check that awesomeness out: they're all amazingly similar.

This is all to be expected, of course. As Martinez & Alcober note, the most primitive dinosaurs are all going to look pretty much alike. But what's really interesting to me is that Panphagia looks a whole lot like Eoraptor. The authors are also impressed by these similarities. Apparently the two taxa share some interesting features, including lanceolate teeth, enlarged external nares, a mandibular joint well below the tooth row, and many others. Additionally, a few "theropod" features present in Eoraptor are shared by Panphagia like hollow limb bones.

So what's all this mean? Among other things, it means that the phylogenetic position of Eoraptor is even more muddled. More importantly, the shared characters of Eoraptor and Panphagia imply that such features are plesiomorphic for Saurischia. But seriously, Panphagia is an incredibly important fossil that demonstrates what characters changed first in the Sauropodomorpha, when Saurischia probably split (Middle Triassic, perhaps?), that the first dinosaurs and their immediate ancestors were probably omnivores, and that the Dinosauria may have originated in Argentina! Seriously, Panphagia protos is a sort of saurischian Archaeopteryx, and that's just too cool.

References (clip 'n' save!):

Martinez, R. N. & Alcober, O. A. (2009). A basal sauropodmorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the early evolution of Sauropodomorpha. PLoS ONE 4(2).

Novas, F. E. (1993). New information on the systematics and postcranial skeleton of Herrerasaurus ischigualastensis (Theropoda: Herrerasauridae) from the Ischigualasto Formation (Upper Triassic) of Argentina. JVP 13(4): 400-423.

Sereno, P. C. & Novas, F. E. (1992). The complete skull and skeleton of an early dinosaur. Nature 258: 1137-1140.

Sereno, P. C., Forster, C. A., Rogers, R. R. & Monetta, A. M. (1993). Primitive dinosaur skeleton from Argentina and the early evolution of the Dinosauria. Nature 361: 64-66.

Sereno, P. C. (1993). The pectoral girdle and forelimb of the basal theropod Herrerasaurus ischigualastensis. JVP 13(4): 425-450.

Sereno, P. C. (1993). The skull and neck of the basal theropod Herrerasaurus ischigualastensis. JVP 13(4): 451-476.


Adam Pritchard said...

Another very cool tidbit about the paper, beyond Panphagia itself, is that the authors mention three more basal dinosaur taxa from the Ischigualasto Formation are yet to be described.

It is also very odd that, when listing the dinosaurs of Ischigualasto, the authors made no mention of Pisanosaurus mertii. A question to its status as an ornithischian, perhaps?

Brad said...

Your last analogy is a bit awkward, since Archaeopteryx is a saurischian too!