Coelophysis (seal-o-fie-sis) was a small, delicately built carnivorous dinosaur that stood two or three feet tall and was about six feet in length. It had a relatively large head (for the body size), long neck, and well-developed forefeet with fingers terminating in small claws. The skull was thin, long, and roughly triangular in shape. Coelophysis was an agile hunter that evidently ate its own young as evidenced by young Coelophysis bones found inside the stomach area of larger skeletons.
Coelophysis lived during the Late Triassic Period in western North America. It is probably the best known Triassic theropod dinosaur as it is represented by many skeletons found at Ghost Ranch in New Mexico. The skeletons were found largely intact and piled one upon the other suggesting that they died in a single catastrophe, probably a flooded river. The presence of so many animals, including some variety in the sizes, suggests possible herding behavior.
Coelophysis is the official State fossil of New Mexico. It has also been known by the name Rioarribasaurus.