Scientists find Tyrannosaurus had three species, not one

A group of three researchers has proposed that the Tyrannosaurus dinosaur actually included three species, and not just the single rex, according to a new study.

A team of three researchers led by Baltimore-based independent paleontologist Gregory Paul on Monday said variations they noticed in an examination of about three dozen Tyrannosaurus fossils warranted the recognition of two additional species: T. imperator, meaning "tyrant lizard emperor," and T. regina, meaning "tyrant lizard queen."

"The variation in Tyrannosaurus is beyond the norms for dinosaurs," said Paul, the lead researcher. "Two new species had occurred before the final dinosaur extinction. The most famous of all dinosaurs and the ultimate apex predator actually includes three species."

Tyrannosaurus rex, meaning "tyrant lizard king," once prowled in North America during the Cretaceous period. The species was wiped out when an asteroid struck Mexico's Yucatan peninsula some 66 million years ago. 

They cited differences in the build of the thighbone or femur, and differences in the number of small teeth at the lower jaw tip among the 37 fossils they examined. 

Paul said the differences were much like the ones between a lion (Panthera leo) and a tiger (Panthera tigris).

Lions and tigers are members of the same genus, Panthera, but have enough differences to be recognized as separate species.

Other experts not convinced

Some scientists not involved with the study have raised doubts over the findings of the research, and said the conclusions will take more persuading. 

"I understand the temptation to divide T. rex into different species, because there is some variation in the fossil bones that we have," Stephen Brusatte, paleontologist at the University of Edinburgh, told the Reuters news agency. 

"It's hard to define a species, even for animals today, and these fossils have no genetic evidence that can test whether there were truly separate populations. Until I see much stronger evidence, these are all still T. rex to me, and that's what I'll be calling them," Brusatte added.

Thomas Carr, a T. rex expert at Carthage College, also disputed the findings, saying they were at odds with his own research in the field. "I found no evidence of more than one species. And if that signal was in the data, I would have picked it up," he was reported as saying in The Guardian.

"Perhaps most damning is the fact that the authors were unable to refer several excellent skulls to any of the three species," Carr said. "If their species are valid, then more than just two features should identify them: Nearly every detail, especially in the head, should be different."

T. rex renowned for its bite

The Tyrannosaurus rex had a very large head and tremendous bite strength. It walked on two legs, and had two small hands with two fingers.

The largest-known Tyrannosaurus is a specimen named Sue at the Field Museum in Chicago, at 12.3 meters * and an estimated 9 tons. The new study suggests that Sue is not a T. rex, but a T. imperator.

Reuters contributed to this article.

Edited by: John Silk