Tyrannosaurus rex may actually be three separate species

After analysing the enamel and thigh bones of 38 T. rex fossils, some researchers suggest reclassifying them as three completely different species, however others are unconvinced

By Colin Barras

The “tyrant lizard king” Tyrannosaurus rex might need belonged to a dynasty. A analysis group has proposed splitting the well-known species into three, with Tyrannosaurus imperator (tyrant lizard emperor) and Tyrannosaurus regina (tyrant lizard queen) taking their locations subsequent to T. rex. But the proposal is already proving unpopular with different palaeontologists.

T. rex was an apex predator that lived in North America between about 68 and 66 million years in the past. The first T. rex fossils had been found greater than a century in the past, however for many years only a few skeletons had been recognized. More have come to mild for the reason that Nineteen Nineties, says Scott Persons on the College of Charleston, South Carolina, which implies it’s now potential to evaluate whether or not or not the animals fall right into a single species.

To discover this query, Persons and his colleague Jay Van Raalte labored with impartial researcher Gregory Paul. The trio checked out bones from 38 T. rex fossils, focusing particularly on two options: the variety of entrance enamel within the decrease jaw and the stoutness of the thigh bones.

They found variation in each options, which they suppose justifies splitting the dinosaurs into three distinct species. The oldest animals which had 4 distinctly small incisors on the entrance of the decrease jaw and the stout thighs of a closely constructed dinosaur are positioned within the new species T. imperator.

The trio imagine this then advanced into two youthful species, each of which had simply two small incisors on the entrance of the decrease jaw. One of those youthful species had slender thigh bones and was evenly constructed it has been named T. regina. The second youthful species had stout thighs and was closely constructed. This species retains the identify T. rex.

There will be those that say youre naming them simply because its intrinsically enjoyable and funky to call a brand new Tyrannosaurus, says Persons, however he argues the choice is justified. He says trendy ecosystems present us that apex predators evolve and diversify into distinct species lions and leopards, for instance and it is extremely seemingly that Tyrannosaurus did so too.

The conclusions have implications for a few of the most well-known Tyrannosaurus fossils, he provides: Sue, a Tyrannosaurus skeleton at the Field Museum in Chicago, is actually T. imperator, whereasStan which was sold to a private buyer for $32 million in 2020 ought to be reclassified as T. regina.

Philip Currie on the University of Alberta, Canada, expects the proposal to stimulate debate. I feel the authors have made a case that there are anatomical modifications within the genus that appear to [change] with time, he says. That is fairly wonderful in itself.

But others will take extra persuading. I perceive the temptation to divide T. rex into completely different species, as a result of there’s some variation within the fossil bones that we’ve got, says Stephen Brusatte on the University of Edinburgh, UK. But finally, to me, this variation could be very minor. Until I see a lot stronger proof, these are all nonetheless T. rex to me.

Thomas Carr at Carthage College in Wisconsin additionally thinks the proof within the new paper is weak. In 2020 he published an in-depth analysis of T. rex. He says his evaluation was structured to uncover patterns within the knowledge, however he discovered nothing that made him suppose there was greater than a single species. I simply suppose theyre seeing what they wish to see, he says.

Not solely does Carr see issues with the evaluation itself, he’s troubled that the three researchers included knowledge from fossils housed on the Black Hills Institute (BHI) of Geological Research, a non-public company in South Dakota.

Carr argues researchers ought to restrict themselves to analysing fossils in public collections, as a result of these specimens will all the time be obtainable for scientific research. Fossils in personal collections have the potential to be offered to somebody who wont enable scientific entry. The BHI was the previous house of Stan earlier than the 2020 public sale.

It is a big downside, says Paul. On the opposite hand, remove all these [BHI] specimens from the pattern and it isn’t potential to evaluate the taxonomy of Tyrannosaurus.

Paul provides that the outcomes of the brand new evaluation would possibly actually assist cut back the probability of fossils being offered in future. He factors out that if a T. rex in a non-public establishment is renamed T. imperator or T. regina, it may not entice as a lot curiosity from potential patrons.

Journal reference: Evolutionary Biology, DOI: 10.1007/s11692-022-09561-5