Eucoelophysis by Moondawg

Eucoelophysis

Eucoelophysis (meaning "true hollow tail") is a genus of dinosauriform from the Late Triassic period of North America. It was assumed to be a coelophysid upon description, but a 2005 study by Nesbitt et al. found that it was actually a close relative of Silesaurus, which was independently supported by Ezcurra (2006), who found it to be the sister group to Dinosauria, and Silesaurus as the next most basal taxon.

However, the relationships of Silesaurus are uncertain. Dzik found it to be a dinosauriform (the group of archosaurs from which the dinosaurs evolved), but did not rule out the possibility that it represents a primitive ornithischian.