Scientists Propose Tyrannosaurus Has Three Species, Not Just “Rex”

WASHINGTON — A group of researchers proposes that Tyrannosaurus, the most famous of all dinosaurs and the ultimate apex predator, actually comprises three species and not just the single T. rex, based on femur and tooth variations among dozens of its fossils.

T. rex, meaning “tyrant lizard king”, is the only recognized species of the genus Tyrannosaurus since the dinosaur was first described in 1905. A genus is a larger grouping of related organisms than a species.

A team of three researchers led by Baltimore-based freelance paleontologist and paleoartist Gregory Paul said Monday (Feb. 28) that variations they spotted in an examination of about three dozen Tyrannosaurus fossils warrant recognition of two additional species: T. imperator, meaning “tyrant emperor lizard” and T. regina, meaning “tyrant lizard queen”.

“After more than a century of all specimens being placed in a species without the matter being carefully considered, the first and only analysis reveals that variation in Tyrannosaurus is beyond the norm for dinosaurs, and is distributed over time. in a way that indicates that Darwinian speciation from one (species) to two new species occurred before the final extinction of the dinosaurs halted evolution,” Paul said.

Tyrannosaurus roamed western North America during the Cretaceous period at the twilight of the Age of Dinosaurs before an asteroid struck Mexico’s Yucatan Peninsula 66 million years ago, condemning the dinosaurs.

Mr Paul and his colleagues cited differences in the sturdiness – some larger and some lighter – of the femur, or femur, and differences in the number of small teeth at the tip of the lower jaw among the fossils examined.

“It is feared that this will be controversial due to the charismatic status of the T. rex, but on the other hand, the study would not receive as much attention otherwise,” said Paul, whose study has was published in the journal Evolutionary Biology. .

Mr. Paul was right about the controversy. Some paleontologists not part of the study disagreed with its findings.

“Ultimately, to me, this variation is very minor and does not indicate a meaningful biological separation of distinct species that can be defined on the basis of clear, explicit, and consistent differences,” said the paleontologist from the University of Edinburgh, Steve Brusatte.

“It is difficult to define a species, even for animals today, and these fossils have no genetic evidence that can test whether there were really separate populations. Until I see much more evidence solid, they’re still T. rexes to me, and that’s what I’m going to call them,” Brusatte added.

Paul did not rule out that differences between individuals or differences between males and females of Tyrannosaurus were at play, but called it unlikely.

Tyrannosaurus had a massive head and enormous bite force, walked on two strong legs, and had puny arms with only two fingers. Perhaps the largest known tyrannosaur is a specimen named Sue at the Field Museum in Chicago, measuring 12.3 meters long and weighing around 9 tons. The new study concluded that Sue is not a T. rex but rather a T. imperator.

The magnitude of the differences between the three proposed Tyrannosaurus species, Paul said, is akin to the differences between a lion – scientific name Panthera leo – and a tiger, scientific name Panthera tigris. Lions and tigers belong to the same genus, Panthera, but have enough differences to be recognized as separate species.

Paleontologist Thomas Carr of Carthage College in Wisconsin, whose 2020 study of T. rex variation found no evidence of multiple species, also differed with the new study.

“Perhaps most damning is that the authors were unable to report multiple excellent skulls from any of the three species,” Carr said. “If their species are valid, then more than two characteristics should identify them: almost every detail – especially in the head – should be different.” Reuters

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