The early ancestors of tyrannosaurus Rex were no bigger than you or me – about one-hundredth the size of the colossal dinosaur we know as T. Rex. EarthSky spoke with Steve Brusatte, a paleontologist at the American Museum of Natural History.
Some of the oldest tyrannosaur fossils we have were only about the size of a golden retriever. In fact, for the first 80 million years of the history of tyrannosaurs, most species didn’t get very big at all. It was only in the final 20 million years that you see this enormous size in the tyrannosaur lineage.
Brusatte said that all tyrannosaurs were predators and walked on two legs. But small arms and large, muscular skulls evolved late in their history. He explained:
The earliest tyrannosaurs had large arms. The earliest tyrannosaurs had pretty small skulls. They had very thin and flimsy teeth. They had very big claws. So they were very different from T. Rex, anatomically and ecologically.
He explained how scientists understand that two different fossils are related – even when they look as different as early tyrannosaurs and the colossal T. Rex.
We look at as many fossils as we can, and we look for characteristics in these fossils that vary from one another. Then we unite groups based upon characters they share. We use computers to help us wade through all these different characters, but the end goal is to find characteristics that organisms share – evolutionary novelties. And organisms that share these characters are more closely related to each other than they are to other organisms.
Brusatte has described what he calls a “family tree” for tyrannosaurs which he created, which puts the lineage of the dinosaurs in perspective.
One of the primary goals of many paleontologists – myself being one of them – is to construct family trees of the animals we study. Because if we have a family tree, it helps us provide context, it helps to interpret our knowledge of a group, just like having a knowledge of our own family history.
Brusatte said there’s still more to learn about tyrannosaurs.
One of the things we’ve done in this paper to summarize knowledge of tyrannosaur biology – not just family tree and evolution – but their biology. How they moved, how they fed, how they reproduced. The goal, from this point forward, is to still keep finding fossils that we can put in the family tree and can teach us more about the big patterns of evolution, but to also to keep working on understanding how T. Rex and other tyrannosaurs functioned as living animals.