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