'One True King': New Study Debunks Claim Of 3 Separate T. Rex Species

Are there really three species of Tyrannosaurus rex, as said by a team of researchers earlier this year? Paleontologists are now refuting the claim, noting that the T. rex is still the "one true king of the dinosaurs."

Researchers published a study on the possibility that there were three, instead of just one, T. rex species in March. They said at the time that most Tyrannosaurus specimens have been attributed to the T. rex species, but "an unusual degree of variation" in the specimens point to the possibility of three Tyrannosaurus species: "the tyrant lizard king, queen and emperor."

They reached the findings based on an analysis of 38 T. rex specimens, the American Museum of Natural History (AMNH) noted in a news release. Among the evidence they highlighted were differences in the size of a tooth in the lower jaw as well as the "robusticity" of the femur.

For the rebuttal paper, published in the same journal as the first study, Evolutionary Biology, Monday, the team of paleontologists looked at the original data as well as measurements from 112 bird species (living dinosaurs) and four non-avian theropod dinosaurs. They concluded that the original study did not provide "sufficient evidence to support the hypothesis that T. rex can be split into three taxa."

"Their study claimed that the variation in T. rex specimens was so high that they were probably from multiple closely related species of giant meat-eating dinosaur," the study's co-lead, James Napoli of the AMNH's Richard Gilder Graduate School, said in the news release. "But this claim was based on a very small comparative sample. When compared to data from hundreds of living birds, we actually found that T. rex is less variable than most living theropod dinosaurs. This line of evidence for proposed multiple species doesn't hold up."

Defining the boundaries between species is really no easy work, even among the living ones, co-author Thomas Holtz of the University of Maryland said, citing the disagreements over the number of current giraffe species. In the case of the T. rex, however, the researchers noted that the differences among the adults could be "best explained by growth and individual variation."

"T. rex is an iconic species and an incredibly important one for both paleontological research and communicating to the public about science, so it's important that we get this right," co-author David Hone of Queen Mary University of London said, as per the news release. "There is still a good chance that there is more than one species of Tyrannosaurus out there, but we need strong evidence to make that kind of decision."

For now, the results of the rebuttal study suggest that there is still only one T. rex species.

"Tyrannosaurus rex remains the one true king of the dinosaurs," co-author Steve Brusatte of the University of Edinburgh said.