Teeth Study Reveals Diversity of Small Dinosaurs in Cretaceous North America

Paleontologist Derek Larson of the Royal Ontario Museum, who spent six years analyzing fossilized dinosaur teeth, has identified more than 20 species of small meat-eating dinosaurs that lived in western North America during the Cretaceous period.

A Troodon, one of the small carnivores characteristic of Alberta dinosaurs, tries to catch a toothed bird (Jan Sovak)

Larson and his research supervisor Prof Philip Currie of the University of Alberta report the findings in a paper in the journal PLoS-ONE.

“Derek was able to expand our identification of small, two-legged meat-eaters that roamed Western Canada and the U.S. from seven species to at least 23,” Prof Currie said.

“These two-legged dinosaurs ranged from the size of a chicken to two meters long. In most cases, tooth fossils are all that remains of small dinosaurs.”

“It’s the same situation you have in today’s world with the remains of small animals like weasels,” Prof Currie said. “Because the bones are light and small in size, after the animal dies the bones scatter, and if they’re not covered by sand or mud they disintegrate very quickly.”

Luckily, the researchers do have fossilized skeletons with teeth for some of the small meat-eaters. For example, Troodon is a two-legged meat-eater about 2 m in length, and Alberta is one area where its fossils have been found.

“We were able to link some previously unidentified fossilized teeth as being from relatives of Troodon,” Prof Currie said. “They were obviously similar teeth, but were not the same. Comparison with other species represented by teeth and bones gave the researchers a way to establish that other tooth samples also must have belonged to small dinosaur species that no one had previously identified.”

The researchers said the huge increase in the number of identified small meat-eating species shows that instead of a few species existing for many millions of years, there were actually many small meat-eating species, each existing for shorter time periods.

“Given that today there are more small animals than large, it’s really not surprising that during the age of the dinosaurs there were lots of small dinosaur species as well,” Prof Currie concluded.

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Bibliographic information: Larson DW, Currie PJ. 2013. Multivariate Analyses of Small Theropod Dinosaur Teeth and Implications for Paleoecological Turnover through Time. PLoS ONE 8(1): e54329; doi: 10.1371/journal.pone.0054329