A new study confutes the bold theory that T. rex was three separate species

The iconic species is still the only giant apex predator.
Deniz Yildiran
Tyrannosaurus Rex Holotype.Wikimedia Commons

Back in March this year, a study published in Evolutionary Biology claimed that fossils categorized as Tyrannosaurus rex represent three separate species. However, a new study published on July 25 in Evolutionary Biology refutes this claim and suggests that the previous research lacked evidence and Tyrannosaurus rex is made of only one species. 

The previously controversial research implied that T. rex should be reclassified as three different species, including the standard T. rex, the bulkier "T. imperator," and the slimmer "T. regina." Researchers analyzed 38 T. rex fossils that contained leg bones and teeth samples, a press release revealed.

However, paleontologists at the American Museum of Natural History and Carthage College were determined to review the data of the previous research, adding data points from 112 species of living dinosaurs—birds—and from four non-avian theropod dinosaurs.

"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," said co-author David Hone from the Queen Mary University of London. "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."

Lack of evidence to suggest T. rex is still the only one

It was clear to researchers that the previous claim didn't have an adequate number of comparative samples, had non-comparable measurements, and had improper statistical techniques. The controversial paper based its claim on the variation in the size of the second tooth in the lower jaw and the robustness of the femur. On the contrary, the new paper's researchers couldn't replicate tooth fossils and came up with different results after measuring the same samples. 

"Pinning down variation in long-extinct animals is a major challenge for paleontologists," said co-lead author Thomas Carr from Carthage College. "Our study shows that rigorous statistical analyses that are grounded in our knowledge of living animals is the best way to clarify the boundaries of extinct species. In practical terms, the three-species model is so poorly defined that many excellent specimens can't be identified. That's a clear warning sign of a hypothesis that doesn't map onto the real world."

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