Effigia

Effigia was an archosaur that lived in what is now New Mexico. The 2 meter (6 ft) fossil was collected by Edwin H. Colbert in blocks of rock from the Ghost Ranch Quarry, which were excavated in 1947 and 1948. However, Colbert did not think any large vertebrates besides basal theropod dinosaurs were present in the quarry and as such did not even open the jackets of most of the blocks that were returned to the AMNH.

Discovery
The fossil was rediscovered in January 2006 by graduate student Sterling Nesbitt at the American Museum of Natural History. Nesbitt was opening jackets of blocks in order to find new specimens of Coelophysis. Upon finding the remains of Effigia, he instantly recognized this was not a dinosaur and proceeded to track down the rest of the blocks from that area of the quarry. Nesbitt and Mark Norell, curator at the museum, named it Effigia okeeffeae in January 2006 after Georgia O'Keeffe, who spent many years at Ghost Ranch (her ashes are scattered there).

Convergence
Effigia is remarkable for its extreme similarity to ornithomimid dinosaurs. Nesbitt, in 2007, showed that Effigia was very similar to Shuvosaurus, and is definitely a member of the crurotarsan group Suchia (in the line leading towards modern crocodilians), and that its similarity to ornithomimids represents a case of "extreme" convergent evolution. Nesbitt also demonstrated that Shuvosaurus was the same animal as Chatterjeea, and that it belonged to an exclusive clade containing closely related suchians such as Shuvosaurus and Poposaurus (Poposauridae). Within this group, Effigia forms an even more exclusive clade with Shuvosaurus and the South American Sillosuchus (Shuvosaurinae).