Fossils Reveal a Possible New Tyrannosaur Species, the Closest Relative of T. Rex

A fossilized partial dinosaur skull originally thought to be from a Tyrannosaurus rex might actually represent a previously unknown species, according to a paper published Thursday in the journal Scientific Reports.

People boating in New Mexico’s Hall Lake Formation found the prehistoric predator’s jaw in 1983, Spencer Lucas, a co-author of the study and paleontologist at the New Mexico Museum of Natural History and Science, tells ABC News’ Julia Jacobo.

Paleontologists later uncovered more of its skull and classified the creature as T. rex. But the shape of its bones, their age and where they were found all point to the dinosaur being of a different species, say the researchers. They have named this creature Tyrannosaurus mcraeensis, after the McRae Formation where it was discovered.

“If a T. rex saw this dinosaur, the one we’ve just named, it would have known it wasn’t dealing with a T. rex,” Lucas says to Scientific American’s Meghan Bartels.

T. rex was an apex predator in its time, living between 66 and 68 million years ago in what is now the western United States. The carnivorous dinosaurs stood 12 feet tall and 40 feet long, and they weighed up to eight tons.

But despite the popular interest in these fierce predators, scientists are unsure where T. rex originated. Paleontologists haven’t dug up any of its close relatives in North America from the time before the species appeared, the study authors write. But T. mcraeensis, as a potential relative of T. rex, could shed light on this question.

Historically, however, the subject of tyrannosaur species has been controversial among scientists. A 2022 paper, for example, suggested that T. rex should be split into three separate species—and this proposal was so disputed that another group of researchers published a rebuttal paper months later. Other experts have spent decades debating whether a certain group of fossils represent T. rex juveniles or another dinosaur entirely.

Similarly, the new paper hasn’t convinced everyone. “I hesitate to regard Tyrannosaurus mcraeensis as being distinct from Tyrannosaurus rex,” Jared Voris, who studies tyrannosaur biology at the University of Calgary in Canada and did not contribute to the findings, tells New Scientist’s Riley Black.

But to the research team, the shape of the New Mexico bones was distinct from those of T. rex. While these differences are subtle—such as less prominent brow ridges on T. mcraeensis—this can often be the case for differences between species, the study authors note.

“The most striking difference is the shape of the lower jaw, which is more slender and curved [than T. rex],” Nick Longrich, a co-author of the study and paleontologist at the University of Bath in England, tells Live Science’s Harry Baker.

Its distinct jaw shape could mean the species ate a different diet than T. rex did. “This animal was likely feeding differently than the big, car-crunching dinosaur of Jurassic Park,” Anthony Fiorillo, a co-author of the study and paleontologist at the New Mexico Museum of Natural History and Science, says to Scientific American.

The reexamined bones also predate T. rex by several million years. Based on the part of the fossil record its remains were found in, T. mcraeensis might have been alive between 70.9 and 72.7 million years ago.

Additionally, the remains were dug up far away from where most T. rex bones have been found, in Montana, Wyoming and South Dakota, per Scientific American. They were also at least 100 miles from the sea coast, while most others have been found much closer to the sea, Lucas says to ABC News.

“We’re looking at a dinosaur fauna that’s living in a rather unique environment,” he tells the publication.

Kat Schroeder, a paleontologist at Yale University who was not involved in the research, tells Scientific American that the animals could have traveled from states in the north to New Mexico.

“An animal the size of T. rex could potentially have an incredibly massive distribution,” she says to the publication. “There’s no reason to think that T. rex couldn’t have been in New Mexico, just based on its physical size.”

The findings suggest tyrannosaurs originated and evolved in the area, the study authors write.

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.