Hairy Museum of Natural History

The catastrophic death assemblage preserved at the Ghost Ranch, New Mexico Coelophysis (Whitaker) Quarry provides a unique opportunity to illustrate a population of Late Triassic theropod dinosaurs. Measurements of 56 individuals at the Quarry suggest a population quite different from those shown in typical illustrations of the “Ghost Ranch Flock.”

Right about now the above text and image should be going up at the PaleoArt Poster Exhibit running alongside the Opening Reception for the SVP Annual Meeting.

Over the past year, I’ve worked with Larry Rinehart to develop skeletal reconstructions of Coelophysis at different growth stages, based on his statistical and allometric studies of the fossils preserved in blocks from the Ghost Ranch Quarry. The preliminary results of that study, and the skeletal reconstructions we’ve developed so far, will be presented during the poster session this Saturday. (For interested readers who aren’t at the conference, check back here when the embargo lifts on Saturday evening for more details.)

One interesting facet that came out of this study was the “demographics” of the Ghost Ranch population—over 40% of the preserved specimens came from small juveniles less than 2kg in weight (like those shown above). Large adults (like AMNH 7223 and 7224, the specimens that most depictions of Coelophysis are probably based on) make up less than 10% of the known specimens of C. bauri. This fits pretty well with the population dynamics of modern crocodiles, and it has some rather dynamic visual implications for artists restoring scenes showing large groups of Coelophysis. I wanted to come up with a quick study portraying this new interpretation of the “Ghost Ranch Flock”

If a population consists of many more children than adults, its a cinch that relatively few Coelophysis hatchlings made it to adulthood. While the case for cannibalism in Coelophysis is still contested, I figured that throwing in an adult grabbing a meal to go in the background would underscore the potential difficulties faced by C. bauri youth. This, along with many other details in the picture, is based on evidence from the NMMNH Coelophysis block—in this instance, some very coelophysoid-looking bones in the coprolites and cololites found aside/inside the skeletons of adults in the block.

—Matt Celeskey.

File under: Dinosaurs, Triassic.