Paleontologists have unearthed a miniature predecessor of Tyrannosaurus Rex, a finding that may rewrite the origins of the most iconic of dinosaurs. “Raptorex,” discovered in China, has all the distinctive features of a Tyrannosaurus—large head and jaws, long legs, and small arms—but it weighed only 150 pounds. The diminutive beast lived 125 million years ago, 35 million years before the more familiar T. Rex.
The existence of Raptorex contradicts a long-held assumption about the development of Tyrannosaurs—that the puny arms and powerful legs came about as the dinosaur increased in size. “The thought was that they needed to modify their entire skeleton so they could function as a predator at such colossal size,” says a researcher at the American Museum of Natural History. Instead, Raptorex suggests that the T. Rex formula gained success in a small package, then scaled up in body size.