Controversial Take: T. Rex Is Actually 3 Species

Tyrannosaurus rex is the most intensively studied dinosaur in the world. Yet generations of paleontologists have failed to notice that T. rex is not a unique species but actually three, according to new research published Tuesday in Evolutionary Biology. "This paper is likely to rock the paleo community, and the public that is so used to good old T. rex," its lead author, independent paleontologist Gregory Paul, tells the New York Times. In analyzing 38 T. rex specimens, he and two colleagues found 26 could be grouped into one of three types: an early, robust form with two sets of incisors in its lower jaws and two later forms—one robust and one gracile—each with one set of incisors.

In their eyes, the variation in these forms, including in the femur, indicate three unique species. The early, robust form is proposed as a new species, Tyrannosaurus imperator or "tyrant lizard emperor," to include the famous Sue kept at Chicago's Field Museum. Over 1 million to 2 million years, researchers say this species split into Tyrannosaurus rex or "tyrant lizard king"—currently the only species in the Tyrannosaurus genus—and the other newly proposed species, the more slender Tyrannosaurus regina or "tyrant lizard queen," to include "the Nation's T. rex" skeleton kept at the Smithsonian National Museum of Natural History. The problem is that many other paleontologists disagree.

Dr. Thomas Carr of Carthage College, who performed an analysis of all known T. rex specimens in 2020, says his data doesn't support the findings. Others say minor differences in body proportion across the three proposed species only suggest change over time. Philip Currie of the University of Alberta is among them, which explains why he chose to remove his name from the study before publication, per the Times. Paul counters that "the variation in Tyrannosaurus is beyond the norms for dinosaurs," equal to that between a lion and a tiger, per Reuters. He adds the pushback is no surprise given T. rex's status. "If it had been a paper about putting another dinosaur into different species, nobody would really care," he tells the Times. (More Tyrannosaurus rex stories.)