Coelophysis was a very early "lizard-hipped" dinosaur.

The best examples of skeletons were found by Edwin Colbert at Ghost Ranch, New Mexico, USA in 1947. Hundreds were found jumbled together in what seems to have been a mass death.

Palaeontologists believe these Coelophysis died of thirst at a dried up water source. The water returned as a flash flood. It buried and preserved their bodies. Phytosaurs, fish, clams and crayfish were also found at the fossil site giving a snapshot of the ecology at the time.

Two distinct forms of Coelophysis have been identified, robust and slender, which palaeontologists believe were male and female. From fossil evidence, palaeontologists have worked out that Coelophysis' legs and feet were long and streamlined, suggesting it was able to run at speed. It had evolved a lighter frame than its ancestors and had no ribs in the back of its torso.

Detailed investigations into its jaw show that it had small teeth. It also had a double hinged lower jaw. With this it could saw its food, although it probably ate small animals whole. It may also have been cannibalistic as the fossilised remains of other Coelophysis have been found in the gut area.