Fossil find suggests dinosaurs not as fierce as thought

A new fossil discovery has led scientists to believe that dinosaurs did not spread throughout the world by overpowering other species, but by taking advantage of a natural catastrophe that wiped out their competitors.

Robert R Reisz, professor and chair of biology at the University of Toronto Mississauga, Tim Rowe, professor of palaeontology at the University of Texas at Austin's Jackson School of Geosciences and Hans-Dieter Sues, curator of vertebrate palaeontology at the National Museum of Natural History in Washington, DC, studied a dinosaur named Sarahsaurus.

"Until recently, we've viewed dinosaurs as very successful animals that outcompeted other species wherever they went," said Reisz.

"But this study puts dinosaurs in a very different light—that they were more opportunistic creatures that moved into North America only when a mass extinction event made eco-space available to them," he added.

One of the five great mass extinction events in Earth's history about 200 million years ago wiped out a lot of dinosaur competitors and evidence suggests that the Sarahsaurus and two other early sauropodomorphs migrated into North America in separate waves long after the extinction and not before.

Sarahsaurus, a 4.3-metre-long bipedal plant-eating animal with a long neck and small head, and weighing about 113 kilograms, lived in what is now the state of Arizona about 190 million years ago, during the Early Jurassic Period.

The results of this research appear in the online edition of the journal Proceedings of the Royal Society B on October 6.