Scientists defend T. rex as the only species of the mighty tyrannosaurus

By Will Dunham

WASHINGTON (Reuters) – T. rex still reigns as king of the dinosaurs, according to scientists who argued on Monday against a controversial hypothesis put forward this year that the mighty carnivore Tyrannosaurus should be recognized as three species, not just one should.

Seven research paleontologists published Monday said a March study offered insufficient evidence that there were three species of Tyrannosaurus based on fossils of the world’s most famous dinosaurs, citing inadequate statistical methods, limited comparative samples and erroneous measurements.

T. rex is the only species of the genus Tyrannosaurus to be recognized since the dinosaur was first described in 1905. A genus is a broader grouping of related organisms than a species.

Three other researchers said in the earlier study, published in the same journal, that three species were identified based on differences in femur thickness and in the shape of the lower front teeth among about three dozen Tyrannosaurus specimens.

“The evidence has to be compelling, and to suddenly separate an iconic animal like T. rex, which has been known for over a hundred years, into different species requires a heavy burden of proof. It’s true that there is variation in the size and shape of T. rex bones, but in our new study we show that this variation is minimal,” said University of Edinburgh paleontologist Steve Brusatte, a co-author of the new study Study published in the journal Evolutionary Biology.

Part of a group called theropods, which includes all carnivorous dinosaurs, Tyrannosaurus had a massive head and tremendous bite force, walked on two strong legs, and had weak arms with only two fingers.

The new study examined within-species variation in femur thickness in four other carnivorous dinosaurs and 112 species of living birds, descendants of small feathered theropods, and found that Tyrannosaurus variation was not exceptional.

“It is normal for each species to vary in size and shape. Just look at the range of heights and waists and wide grins of today’s humans, all members of a single species. So the differences between the bones and teeth of T. rex are so insignificant that they don’t support the division of T. rex into multiple species,” Brusatte said.

Tyrannosaurus roamed western North America during the Cretaceous twilight of the Dinosaur Age, before an asteroid struck Mexico’s Yucatan Peninsula and wiped out the dinosaurs 66 million years ago.

“Tyrannosaurus rex remains the one true king of dinosaurs. It’s the only species of giant apex predatory dinosaur that lived in North America at the end of the Cretaceous period,” Brusatte added.

In addition to the species T. rex, meaning “tyrant lizard king,” Baltimore-based independent paleontologist and paleoartist Gregory Paul and two colleagues proposed two other species: T. imperator, meaning “tyrant lizard emperor,” and T. regina , meaning “tyrannical lizard queen.”

Paul criticized the new work as hastily done and “not a proper scientific study”.

“It comes across as paleopropaganda that seems structured to defend T. rex rather than seriously investigating the possibilities that fossil specimens of the genus Tyrannosaurus contained more than one species, which the genus certainly had,” Paul said.

“There’s something about the beloved T. rex that excites people to a degree that other paleotaxa (ancient organisms) don’t. For example, had our work related to the species of the equally gigantic Argentine theropod Giganotosaurus, it most likely wouldn’t have been so much fuss and effort,” added Paul.

Perhaps the largest known tyrannosaurus is a specimen named Sue in the Field Museum in Chicago, which is 12.3 meters long.

“We’re open to the possibility that there are multiple species of Tyrannosaurus,” Brusatte said. “We just need more and better fossils. The number of fossils in their data set is so small that it is difficult to find a consistent way to divide Tyrannosaurus into multiple species based on clear, easily defined, consistent differences.”

(Reporting by Will Dunham; Editing by Lisa Shumaker)

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