WASHINGTON • A newly discovered cousin of the T. rex may explain how the legendary dinosaur leapt in size to become undisputed king of the food chain.
At the end of the dinosaur age 65 million years ago, Tyrannosaurus rex was a behemoth killer animal, up to 12m long and weighing several tonnes.
The very first tyrannosaurs, which appeared about 100 million years earlier, were small, about the size of an average human. The evolutionary jump of tyrannosaurs from people- and horse-size to behemoths has remained a mystery.
The bones of Timurlengia euotica, uncovered in Uzbekistan where it lived about 90 million years ago, provide a clue: It has many of the giant's characteristics, but not its stature or heft. The previously unknown relative of the T. rex was far smaller, but had already developed the large brain it needed to track and devour prey. Its features help illustrate how small tyrannosaurids evolved to grow smarter and larger, thanks to keen senses that helped keep their bellies filled.
"The ancestors of T. rex would have looked a whole lot like Timurlengia - a horse-sized hunter with a big brain and keen hearing that would put us to shame," said Dr Steve Brusatte of the University of Edinburgh's School of GeoSciences. "Tyrannosaurs had to get smart before they got big."
Not much is known about how the T. rex got so big, "largely because of a frustrating 20-plus-million-year gap in the mid-Cretaceous fossil record," said the study, published on Monday in the Proceedings of the National Academy of Sciences.
AGENCE FRANCE-PRESS, NEW YORK TIMES