Coelophysis was an active and agile, bipedal predator that lived on the river floodplains of Late Triassic New Mexico, about 205 to 210 million years ago. The skeleton of a large (adult) Coelophysis is about 3 meters (9.8 feet) long and a maximum weight estimate for the adult dinosaur is about 45 kilograms (100 pounds).
The skull of Coelophysis has more than 100 pointed, serrated, blade-like teeth—the dentition of a meat eater. The major bones of the skeleton are hollow and slender, and the hind limbs are more than twice the length of the forelimbs. Based on comparisons to modern lizards and birds, these features indicate that Coelophysis lived on the ground (not in the trees) and walked on its hind limbs (a biped).
The long and slender tail of this Late Triassic dinosaur acted as a counterbalance to the dinosaur’s body while running, when the body was held nearly horizontal to the ground. The light body weight and slender bones suggest that Coelophysis was very active, fast and agile. The long neck, with its swivel joint at the base of the skull, and the relatively large eyes, characterize a visual predator, much like modern birds of prey.
The forelimbs of Coelophysis are short, but the hands are relatively large and have three functional, clawed fingers. This indicates that Coelophysis used the hands to grasp or hold its prey items, which included small animals, such as early mammals and lizard-sized primitive reptiles, as well as its own young (Coelophysis was a cannibal).
At Ghost Ranch in northern New Mexico, hundreds of skeletons of Coelophysis are in a single fossil bone bed. This suggests to paleontologists that many Coelophysis were killed in a single catastrophe, and that the dinosaur may have lived in some sort of social group.