Scientists propose Tyrannosaurus had three species, not just 'rex'

By Will Dunham

WASHINGTON – A gaggle of researchers is proposing that Tyrannosaurus, probably the most well-known of all dinosaurs and the final word apex predator, really consists of three species and never simply the one T. rex, primarily based on thighbone and tooth variations amongst dozens of its fossils.

T. rex, that means “tyrant lizard king,” has been the only species of the genus Tyrannosaurus acknowledged for the reason that dinosaur was first described in 1905. A genus is a broader grouping of associated organisms than a species.

A staff of three researchers led by Baltimore-based impartial paleontologist and paleoartist Gregory Paul on Monday stated variations they noticed in an examination of about three dozen Tyrannosaurus fossils warranted the popularity of two extra species: T. imperator, that means “tyrant lizard emperor,” and T. regina, that means “tyrant lizard queen.”

“After over a century of all specimens being positioned into one species with out the difficulty being rigorously examined, the primary and solely evaluation finds that the variation in Tyrannosaurus is past the norms for dinosaurs, and is distributed over time in a way that signifies that Darwinian speciation from one (species) to 2 new species had occurred earlier than the ultimate dinosaur extinction lower off additional evolution,” Paul stated.

Tyrannosaurus prowled western North America throughout the throughout the Cretaceous Interval on the twilight of the dinosaur age earlier than an asteroid struck Mexico’s Yucatan peninsula 66 million years in the past, dooming the dinosaurs.

Paul and his colleagues cited variations within the robustness – some bigger and others extra calmly constructed – of the thighbone, or femur, and variations within the variety of the small tooth on the decrease jaw tip among the many examined fossils.

“It's a concern that this might be controversial due to the charismatic standing of T. rex, however then again the research wouldn't be getting a lot consideration in any other case,” stated Paul, whose research was revealed within the journal Evolutionary Biology https://hyperlink.springer.com/article/10.1007/s11692-022-09561-5.

Paul was right about controversy. Some paleontologists not a part of the research disagreed with its conclusions.

“Finally, to me, this variation could be very minor and never indicative of significant organic separation of distinct species that may be outlined primarily based on clear, express, constant variations,” College of Edinburgh paleontologist Steve Brusatte stated.

“It’s onerous to outline a species, even for animals at this time, and these fossils don't have any genetic proof that may take a look at whether or not there have been really separate populations. Till I see a lot stronger proof, these are all nonetheless T. rex to me, and that’s what I’ll be calling them,” Brusatte added.

Paul didn't rule out that variations amongst people or variations between Tyrannosaurus men and women had been at play, however referred to as this unlikely.

Tyrannosaurus had an enormous head and large chew energy, walked on two robust legs, and had puny arms with simply two fingers. Maybe the largest-known Tyrannosaurus is a specimen named Sue on the Subject Museum in Chicago, at 40-1/2 toes (12.3-meters) lengthy and an estimated 9 tons. The brand new research concluded that Sue isn't a T. rex however slightly a T. imperator.

The dimensions of the variations among the many three proposed Tyrannosaurus species, Paul stated, is akin to the variations between a lion – scientific identify Panthera leo – and a tiger, scientific identify Panthera tigris. Lions and tigers are members of the identical genus, Panthera, however have sufficient variations that they're acknowledged as separate species.

Paleontologist Thomas Carr of Carthage School in Wisconsin, whose 2020 research of variation https://peerj.com/articles/9192 in T. rex discovered no proof of a number of species, additionally differed with the brand new research.

“Maybe most damning is the truth that the authors had been unable to refer a number of wonderful skulls to any of the three species,” Carr stated. “If their species are legitimate, then extra than simply two options ought to determine them: almost each element – particularly within the head – must be totally different.”