Dino of the Week: Coelophysis

Type Species: Coelophysis bauri

Classification: Dinosauria - Saurischia - Theropoda - Coelophysoidea - Coelophysidae 

Time Period: Late Triassic to Early Jurassic

Location: Southwestern U.S.A. and Africa

Diet: Carnivore

Coelophysis fossils have been found in the southwestern United States and in South Africa and Zimbabwe. It was a small, slender bipedal carnivore that could grow up to nearly ten feet in length and was about three feet in height at the hips. It appeared in the Upper Triassic of the Norian stage and survived through the Triassic-Jurassic extinction before dwindling to extinction in the Jurassic. Coelophysis probably weighed around forty pounds and was a fast, agile runner. Coelophysis’ anatomy was advanced from that seen in the Carnian-era’s Eoraptor and Herrerasaurus, and the type species (Coelophysis bauri) already had a wishbone (the earliest example in dinosauria, and which would become a central piece of bird anatomy). Coelophysis’ forelimbs were designed for grasping prey. The long tail had an unusual structure within its interlocking prezygapophysis (the ‘pipe-fitting’ of vertebrae) creating a semi-rigid lattice that prevented the rigid tail from moving up and down. Its head was nearly a foot long with large, forward-facing eyes that provided stereoscopic vision and excellent depth perception. Its sclerotic rings indicate that it was a diurnal (it was most active during daytime and likely slept at night). A study of its sclerotic rings further indicate that its vision was far superior to that of lizards and ranked up with those of birds of prey; Coelophysis’ orbital structure closely resembles those of eagles and hawks. It probably had poor night vision.

Gregarious behavior for Coelophysis is hotly debated

Coelophysis’ teeth indicate it was carnivorous: the teeth were blade-like and recurved with sharp, jagged serrations. It likely preyed on small, lizard-like animals, and many scientists believe it could run in packs and coordinate with others of its pack to bring down larger prey; however, because its forelimbs – despite a wide range of motion – were weak, and because its teeth were relatively small, it’s likely that it spent most of its time chasing after small prey. This doesn’t mean, of course, that Coelophysis wasn’t gregarious: the Ghost Ranch bone-bed of New Mexico contains over a thousand of Coelophysis remains, and it may very well  be that Coelophysis ‘flocked’ like modern birds. Another theory is that Coelophysis generally hunted on their own but congregated around watering-holes. It may be the case that Ghost Ranch is the scene of a one-up tragedy: while gathering together to feed on a spawning run of fish before being buried in a catastrophic flash flood. Proponents of gregarious behavior among Coelophysis point to sexual dimorphism as evidence: two ‘morphologies’ of Coelophysis exist, and these may indicate a male or female species. Dimorphism among a species usually indicates gregarious behavior, and a further study of sexual dimorphism among this dinosaur showed that the different morphologies were split close to half-and-half of the population – exactly what you’d expect in a gregarious social hierarchy. A wrench in the theory, however, is the growth rates of Coelophysis: hatchlings grew rapidly during the first year of life and likely reached adulthood by their third birthday. Such fast growth is seen in animals that need to fend for themselves upon birth. A 2009 comparative study between Coelophysis and modern birds and reptiles indicates that Coelophysis laid between 24-26 eggs in each clutch and that parental care was necessary to nurture the relatively small hatchlings during the first year of life. When all these threads come together, there’s no consensus on whether Coelophysis was gregarious – further study (and discoveries) are needed.

a lone Coelophysis on the prowl