“We know more about tyrannosaurs than any other group of dinosaurs-even more than some groups of living organisms,” says Stephen Brusatte, a graduate student affiliated with the Museum and first author of the paper. “Over the past year, five new species of tyrannosaurs have been described, and over the last ten years we have found the oldest and smallest members of the group. Now we can understand the family tree of tyrannosaurs in unprecedented detail.”

 The Science paper combines a new analysis of tyrannosaur phylogenetics, or their genealogy, with a review of recent research into their biology. After scoring 19 well-documented tyrannosaur fossils for over 300 different traits, the researchers developed the most comprehensive evolutionary tree of this group to date. This essentially redefined tyrannosaurs, at least when compared to the popular perception of them as large meat-eaters. Tyrannosaurs have a long evolutionary history of which the largest, T. rex, Albertosaurus, and Tarbosaurus, represent species that were ecologically dominant only during the Late Cretaceous in Asia and North America. Earlier tyrannosaurs, on the other hand, lived up to 100 million years before the large apex (top) predators, which were often small in size (some one-one hundredth of the size of T. rex and akin to a lynx in body mass), and lived all over the world.

“T. rex is really just the tip of the iceberg of tyrannosaur diversity, and honestly, is quite abnormal when compared with other members of the group. For most of their evolutionary history, tyrannosaurs were small and living in the shadow of other giant apex predators,” says Brusatte. “They stayed small until the end of the Cretaceous-the final 20 million years of dinosaur history.”