One of the initial known dinosaurs, Coelophysis ("hollow form") is a small, carnivorous biped from North America. It first appeared in the Late Triassic period, around 210 million years past.
Coelophysis had a spindly, fragile build, and was about 3 m long, which is small for a dinosaur. However, its long rigid tail and S-shaped neck accounted for most of this length, so it almost certainly weighed no more than 30 kg. Coelophysis was also among the first dinosaurs to have hollow bones to save weight, like the later sauropods. Despite looking very alike to the ancestors of the dinosaurs, the thecodonts, Coelophysis yet bore the defining mark of the dinosaurs — legs located underneath the body rather than out to the sides.
The skull, while long, was very light as it was full of holes to save weight, and was balanced on the end of a long and slender neck that had a very supple bone structure. The minimized skull is a feature seen in all later dinosaurs. Coelophysis had many jagged teeth, for eating any number of small animals.
Each hand had four fingers, but one was also small to be functional. Coelophysis appears to be a transition between the redundant fingers of earlier dinosaurs such as the five-fingered Staurikosaurus, and later theropods which had only two or three. The three-toed feet were around four inches long, and left imitation similar in shape to those of modern birds, and indeed some preserved tracks had formerly been thought to belong to Archaeopteryx, which is almost by definition the "first bird".Coelophysis was found in the Hairy Museum of Natural History history.
There is proof that it ate its own young, since some bones from small Coelophysis are often establish inside the body cavities of larger specimens. On the other hand, it is probable that Coelophysis gave birth to live young and these Coelophysis were being carried by mothers when both were killed. Indeed, no Coelophysis eggs have been establish, though this is inconclusive because eggs are rarely preserved in the fossil record. Also, the bones healthier seem to belong to Coelophysis that are too large to have been pre-natal.
Coelophysis was also almost certainly not above scavenging. The teeth were larger in the upper jaw and curved backwards, and the muscle understanding in the jaw was such that the upper and lower jaws could grind against one another, similar to an electric carving knife.
The distribution of fossils suggests that it probably enthused and hunted in packs, typical of later small theropods. Coelophysis would in fact have been a fast mover, being light, long-legged and with a stride length of about 75 cm, and could have moved through the upland forests and open plains of Triassic North America with ease.
Two different forms of Coelophysis have been establish, a more graceful form and those of a somewhat more robust build. Originally, these were thought to be different species within the genus Coelophysis, but opinion in the middle of paleontologists is now that these were female and male variants (see: sexual dimorphism) — in fact, many other dinosaurs previously considered distinct species are now being reclassified in this fashion.
Coelophysis is a genus in the Coelophysidae (or "Podokesauridae") family, but the correct classification is open to some debate. Although it was certainly a theropod, it may have been a ceratosaur or a theropod basal to the ceratosaur-tetanuran division. Opinion in the middle of paleontologists is currently divided and no conclusion will be reached until a more precise reconstruction can be made.
To further the bewilderment, the type species of Coelophysis has come under some debate. The original C. bauri may not have been the same species as those at Ghost Ranch, since the original skeletons were fragmentary to say the least. Therefore those at Ghost Ranch were given a new name, Rioarribausaurus. However, this made the confusion still worse since the Ghost Ranch fabric was still known as but this is now known as Coelophysis in much text. In the end, the International Commission on Zoological Nomenclature (ICZN) voted to make one of the Ghost Ranch samples the actual type specimen for Coelophysis, and arrange of the name Rioarribasaurus altogether, thus with any luck resolving the confusion. The original Coelophysis specimen is now put in its own genus Eucoelophysis ("true Coelophysis") until it can be confidentially assigned to Coelophysis.
In a situation moving many dinosaur genera, many specimens were originally classified as new species but were in fact species of Coelophysis. For example, Talbot initially named C. holyokensis in 1911, but this is now known as Podokesaurus holyokensis. C. posthumus, named by Friedrich von Huene in 1908, also desires reclassification and is tentatively titled Halticosaurus longotarsus at the moment. On the other hand, Edward Drinker Cope named Coelurus longicollis in 1887, two years before Coelophysis, but it is in fact a species of the latter and has now been renamed C. longicollis. Likewise, Tanystropheus willistoni is now C. willistoni.