| Named By: | R. M. Sullivan & S. G. Lucas in 1999 |
| Time Period: | Late Triassic, 228-208 Ma |
| Location: | USA, New Mexico - Chinle Formation |
| Size: | Roughly estimated at about 1.4 - 1.5 meters long |
| Diet: | Carnivore |
| Fossil(s): | Partial remains of at least two individuals |
| Classification: | | Chordata | Reptilia | Dinosauromorpha | Dinosauriformes | Silesauridae | |
Eucoelophysis (meaning "true hollow form") is a genus of dinosauriform from the Late Triassic (Norian) period Chinle Formation of New Mexico. It was assumed to be a coelophysid upon description, but a 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.