Fossil bones discovered in a jungle stream bed in Thailand have revealed the oldest known tyrannosaur, a meat-eater that gnashed its teeth 50 million years before the much larger Tyrannosaurus rex, scientists reported Thursday.
The animal apparently roamed some 120 million to 130 million years ago, researcher Eric Buffetaut said. That's at least 20 million years older than what had been the oldest tyrannosaur remains, scanty traces from central Asia and perhaps North America.The discovery strengthens indications that tyrannosaurs evolved in Asia and spread to North America over a land bridge across the Bering Strait.
The newfound creature measured about 21 feet from its nose to the tip of its tail, about half the length of T. rex, which lived in North America about 50 million years later.
The Thai creature apparently had curved and serrated teeth up to 4 inches long and fed on plant-eating dinosaurs that were about twice its size and probably much heavier, Buffetaut said.
Tyrannosaurs were not the only big meat-eating dinosaurs to run on two legs. But they were distinguished by such traits as very short arms with only two fingers and skulls full of hollow pockets like a bird's. About a dozen tyrannosaur species are known, all from Asia and western North America.
The newfound creature probably looked like a smaller version of T. rex, weighing a couple tons, Buffetaut said.
Buffetaut, a paleontologist at the National Center for Scientific Research in Paris, reported the finding Thursday in the journal Nature with colleagues there and in Thailand.
They dubbed the dinosaur Siamotyrannus isanensis, which incorporates Thailand's old name of Siam and the local name for the northeastern part of Thailand, Isan.
They recovered the left half of the pelvis, the backbone structure called the sacrum and 18 vertebrae, mostly from the tail. Several features of the pelvis identify the creature as a tyrannosaur, Buf-fe-taut said.
In earlier finds from the same general area, remains of plant-eating dinosaurs had been recovered together with a few teeth that clearly came from a meat-eater. The meat-eater's teeth - serrated like a steak knife - probably came from Siamotyrannus, Buffetaut said.
Thomas Holtz Jr., a vertebrate paleontologist at the University of Maryland, agreed that the creature appeared to be a tyrannosaur. But it would be nice to have a skull to make sure, he said.