Before the discovery of Eoraptor and Heliosaurus, Coelophysis was considered the earliest theropod dinosaur. In northern New Mexico, USA, scientists discovered an exceptionally complete and perfectly preserved Coelophysis skeleton in Late Triassic strata, suggesting that Coelophysis can indeed be considered a representative of early theropod dinosaurs.
Coelophysis
Coelophysis was nearly 2.5 meters long, with a light body and hollow bones, much like a bird. Therefore, it is estimated that it weighed around 20 kilograms when alive. Coelophysis was a typical bipedal animal, with strong, bird-like hind legs well-suited for walking. Its forelimbs were short, possessing dexterous hands adapted for climbing and catching prey. It balanced itself on its hips, and had a long, thin tail. Its neck was also quite long, ending in an intricately structured skull.
The Coelophysis had a long, narrow skull with a large temporal foramen and anterior eye sockets. These features laid the morphological foundation for the entire theropod dinosaur family. The Coelophysis's laterally flattened teeth were deeply embedded in the alveoli, extremely sharp, and serrated. Such teeth reveal the Coelophysis's highly carnivorous nature; they likely fed on small or medium-sized reptiles.
The pelvic girdle of Coelophysis displays typical saurischian features. The ilium expands forward and backward and connects to a long sacrum containing several vertebrae; the pubis extends forward and downward from both sides of the ilium, while the ischium extends backward and downward; both the pubis and ischium are relatively long, especially the pubis, and they are joined to the ilium by a bony protuberance rather than being directly connected; the acetabulum (articular socket) that houses the spherical femoral head is perforated or penetrating, a feature that distinguishes all dinosaurs from other reptiles.
The lifestyle of Coelophysis likely represents a fundamental adaptation of theropod dinosaurs: a preference for living in dry, high-altitude environments. In such conditions, the ability to run quickly and move nimbly were paramount, both for hunting prey and escaping enemies. Coelophysis laid the foundation for theropod dinosaur adaptations in this respect.
