At 243 million years old (Late Anisian, Early Middle Triassic), Nyasasaurus parringtoni, was yesterday promoted as a possible world’s oldest dinosaur. Found in the 1930s, described in the 1950s, it was recently redescribed from a museum shelf by Nesbitt et al. (2012) as the oldest known member of, or the sister-taxon to, the Dinosauria.
According to Wiki, dinosaur traits in Nyasasaurus include the long deltopectoral crest with a deflected top on the humerus, elongated cervicals with hollowed-out lateral portions; and, perhaps, the possession of three sacral vertebrae instead of two.
The large reptile tree includes Lotosaurus among the Dinosauria at 240 million years ago, so not as old. An ancestral taxon, Vjushkovia, was a contemporary. Euparkeria was older at 247 million years ago, along with some – but not all – of the more primitive known taxa. Even Proterosuchus at the base of the Archosauriformes goes back only to 250 million years ago. That’s a lot of variation in a very short amount of time.
So, there was lots of evolution somewhere, or everywhere, in the Early Triassic! The Dinosauria likely originated in Tanzania or elsewhere thousands to millions of years earlier than Nyasasaurus today represented by a single partial fossil -probably- from among the millions of Nyasasaurus living back then.
I won’t be able to provide a cladistic analysis with so few bones known, but having three sacrals points to something other than dinosaurs since Herrerasaurus and basal phytodinos like Pampadromaeus have only two. The long neck could be dinosaurian. It would also be worthwhile to compare that humerus to Decuriasuchus, a basal archosaur from 240 mya, closer to basal Rauisuchia and basal crocs.
Nyasasaurus is certainly a key taxon at the cusp of several important clades. Let’s hope more material comes out soon.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.
Charig AJ 1956. New Triassic archosaurs from Tanganyika, including Mandasuchus and Teleocrater. Dissertation, Cambridge University.
Nesbitt SJ, Barrett PM, Werning S, Sidor CA and Charig AJ 2012. The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania. Biology Letters. online