Late Triassic – Early Jurassic
Of all the many theropod dinosaurs collected worldwide, Coelophysis bauri from North America is probably one of the better understood. It appeared early in the story of dinosaur evolution, demonstrating a successful bipedal body plan that would advantage theropod dinosaurs over their more diverse archosauriform contemporaries and ultimately give rise to successful radiations of larger carnivorous dinosaurs beyond the late Triassic.
Although discovered in North America, Coelophysis and other coelophysoid dinosaurs weren’t limited to this single geographical location. Indeed, with the super continent Pangaea still intact through much of their evolution, coelophysoid remains have been discovered in both northern and southern hemispheres, with another well represented species, C. rhodesiensis recognised from southern Africa. Other fossils have been found in France, Germany and even Antarctica and a probable coelophysis-like tooth was found on the Isle of Skye in Scotland.
Coelophysis bauri was a lightly-built dinosaur averaging lengths of three metres, and is known from literally hundreds of skeletons, having been excavated in large concentrations at a mass grave-site in Arizona. This prompted palaeontologists to speculate that Coelophysis was a gregarious animal and travelled in packs, perhaps hunting together to subdue larger prey; this is a possible hypothesis, although to date, no evidence to support this behaviour exists. It is probable also that environmental forces, such as a drought or flash flood or indeed dietary interests like fishing, may have concentrated these animals together, and this idea is further supported within the Coelopyhsis anatomy by the presence of kinked snouts and conical dentition in the premaxilla and tip of the lower mandible, ideal for picking up small or slippery prey.
Another interesting observation difficult to make with many dinosaurs, but thought possible with Coelophysis due to the abundance of fossil remains, is the probability of demonstrating sexual dimorphism; there being both gracile and a robust forms present in equal numbers at the mass gravesite, however, more recently, research would suggest this particular dinosaur displayed great variation in its adult and juvenile growth rates and the idea of obvious sexual dimorphism has been rejected pending more compelling evidence.
In terms of life appearance, Coelophysis was a primitive dinosaur, retaining four digits on its hand, short arms, short legs and a reptilian-like ribcage; yet had already evolved several bird-like features, including a pneumatic skeleton. Coelophysis evolved during the late Triassic era when the world’s average temperatures were higher than today, yet we cannot say for certain whether this small, primitive dinosaur had an armoured, scaly or possibly an early protofeather integument.
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