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|Pronunciation||See - Lo - Fy - Sis|
Coelophysis was one of the early dinosaurs. They lived in mid to late Triassic period, and had some physical features that were different from the other dinosaurs. But generally, Coelophysis shows that the dinosaur structures in general had developed a lot since Eoraptor and Herrerasaurus.
Coelophysis was far too small to be a one of the 'big carnosaurs', and far from being the King of his time. They were small and light. In fact, the name Coelophysis means hollow form. It means the bones were hollow, and that would make them very light.
Why were they considered fast? Well, the bones in the backbone (vertebral bones) had special locks holding them in place in the tail. This meant the tail could not swing up and down (it could swing sideways). No tail swing (up and down) meant that he could run fast. (When the tail swings up and down, energy is lost to this motion and running would slow down. It is like a bicycle. A rigid frame makes the bicycle faster, though it's a bumpier ride.) With this rigid frame, Coelophysis could run fast.
Another feature that helped them run fast was the hollow bones. Since they were hollow, they were lighter than animals with bones that were not hollow. But at the same time, since they were round, these bones were still strong. (Think about the center of toilet paper. The cardboard tubes are hollow to save weight, but they are still strong enough to give form to the toilet paper.)
The common image of this dinosaur is hunting in packs. This is because of one discovery in New Mexico on the Ghost Ranch. Hundreds of Coelophysis fossils were found all together (along with some other species). The common thought here is that these animals were all together and some small catastrohe like a flash flood swept them all to their deaths at the same time. Similar things have been known to happen today when large herds of animals cross rivers. As a result, the image of Coelophysis is hunting in packs. If this were the case, they could indeed be very scary. Imagine a pack of reptiles, each three meters long, running fast, with sharp claws and lots of razor sharp teeth (pointy with two cutting edges). Scary.
What? Cannibals? Well, in fact, Coelophysis is now not considered a cannibal by most authorities, although they were for a while. They bones of one Coelophysis showed another younger one inside the abdominal cavity (where the stomach is). Many scientists accepted that this showed one Coelophysis had eaten another. Now, recent studies (two, studies, both well done) show that in fact, it was another kind of reptile, and a mistake had been made.
We no longer think of Coelophysis as a cannibal but it made for good stories for a while.
Coelophysis had four fingers, which is one more than most dinosaurs. One of the fingers was already vestigial (that means it has become small and already lost its use), and was probably covered by skin.
The significance of the number of fingers that Coelophysis had is that the number of fingers on dinosaurs changed over time. This dinosaur - one of the earliest - had four fingers, but by the time they got to Tyrannosaurus rex, it was already down to two fingers. That plus on this dinosaur, even though it had four fingers, only three functioned. The number of fingers on dinosaurs, then, appears to decrease with time and evolution.