Sarahsaurus: the not-so-fierce dinosaur

Sarahsaurus: the not-so-fierce dinosaur

What if dinosaurs weren’t the fierce, migratory conquerors conventional wisdom makes them out to be?

A newly identified species of dinosaur, Sarahsaurus (named after Sarah Butler, for whom UT’s Sarah and Ernest Butler School of Music is named), paints a kinder, gentler picture of how dinosaurs entered North America from their original home in the south. Signs indicate these dinosaurs relied more on natural catastrophe than brute force to pave their way.

Sarahsaurus, a sauropodomorph, lived about 190 million years ago during the Early Jurassic Period. It was 14 feet long and weighed about 250 pounds.

At the end of the Triassic Period 200 million years ago, one of the five great mass extinction events in Earth’s history wiped out many of the potential competitors to dinosaurs. Evidence from Sarahsaurus and two other early sauropodomorphs suggests that each migrated into North America in separate waves long after the extinction and that no such dinosaurs migrated there before the extinction.

This belies the commonly held belief that dinosaurs moved up from South America using their size and ferocity to overpower other creatures in their paths.

Tim Rowe, professor of paleontology at The University of Texas at Austin’s Jackson School of Geosciences, and co-authors Hans-Dieter Sues, curator of vertebrate paleontology at the National Museum of Natural History in Washington, D.C., and Robert R. Reisz, professor and chair of biology at the University of Toronto, published this description in the online edition of the journal Proceedings of the Royal Society B on Oct. 6.

Sarahsaurus had physical traits usually associated with gigantic animals. Its thigh bones were long and straight like pillars yet were not much larger than a human’s thigh bones. Its hands were smaller than a human’s hands but much more powerful with large claws.

Sarahsaurus shows that sauropodmorphs started out small and later evolved to a very large size, leading scientists to reconsider some of their previous ideas about how size and evolution work.

A team of researchers and students led by Rowe discovered Sarahsaurus on a field trip in Arizona in 1997. The research was funded in part by an Assembling the Tree of Life grant from the National Science Foundation.