“Bold Theory” That T. rex Was 3 Species Rebutted – “Tyrannosaurus rex Remains

As part of the Museum’s temporary exhibition T. rex: The Ultimate Predator, which was on view from 2019-2021, visitors encountered a massive life-sized model of T. rex with patches of feathers—the most scientifically accurate representation of T. rex to date. Credit: D. Finnin/ ©AMNH

Paleontologists find insufficient evidence that the iconic Tyrannosaurus rex should be reclassified.

A bold assertion made earlier this year that fossils identified as belonging to the dinosaur Tyrannosaurus rex really represent three distinct species is debunked by new research. The rebuttal finds that the earlier proposal lacks sufficient evidence to split up the iconic species. The study is published today (July 25, 2022) in the journal Evolutionary Biology and led by paleontologists at the American Museum of Natural History (AMNH) and Carthage College.

“Tyrannosaurus rex remains the one true king of the dinosaurs,” said study co-author Steve Brusatte, a paleontologist at the University of Edinburgh who conducted his Ph.D. work at the Museum. “Recently, a bold theory was announced to much fanfare: what we call T. rex was actually multiple species. It is true that the fossils we have are somewhat variable in size and shape, but as we show in our new study, that variation is minor and cannot be used to neatly separate the fossils into easily defined clusters. Based on all the fossil evidence we currently have, T. rex stands alone as the single giant apex predator from the end of the Age of Dinosaurs in North America.”

In March 2022, authors of the controversial study made the case that T. rex should be reclassified as three species: the standard T. rex, the bulkier “T. imperator,” and the slimmer “T. regina.” The study, which was also published in the journal Evolutionary Biology, was based on an analysis of the leg bones and teeth of 38 T. rex specimens.

An illustration of a T. rex feeding. Credit: © Mark Witton 2022

In the new paper, scientists revisited the data presented in the earlier study and also added data points from 112 species of living dinosaurs—birds—and from four non-avian theropod dinosaurs. According to their findings, the multiple species argument was based on a limited comparative sample, non-comparable measurements, and improper statistical techniques.

“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,” said James Napoli, co-lead author of the rebuttal study and a graduating doctoral student in the Museum’s Richard Gilder Graduate School. “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.”

“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…