A new study challenges the controversial claim made earlier this year that fossils classified as Tyrannosaurus rex represent three different species.
The replication, published recently in the journal Evolutionary Biology and coordinated by paleontologists at the American Museum of Natural History and Carthage College, Wisconsin, USA, shows that the earlier proposal lacks sufficient evidence to separate the known species from the dinosaur.
“Tyrannosaurus rex remains the true king of dinosaurs. Recently, a bold theory has been promulgated with great fanfare, namely that what we call T. rex was actually composed of several species. While it is true that the fossils vary in shape and size, as we show in our study, this variation is minor and cannot be used to divide the fossils into easily defined groups. Given the current fossils we have, T. rex remains a single top predator from the end of the age of dinosaurs in North America,” said Steve Brusatte, a paleontologist at the College of Edinburgh in the United Kingdom.
In March 2022, the authors of the controversial study, also published in the journal Evolutionary Biology, argued that T. rex should be divided into three species: T. rex, T. imperator and T. regina. The study was based on analysis of bones and teeth from 38 T. rex specimens, EurekAlert said.
The authors of the new study revised data from the earlier study and added data from 112 other living dinosaur species (birds) and four non-avian dinosaurs. They found that the multiple species argument was based on a comparatively limited sample, non-comparable measurements and flawed statistical procedures.
“Their study claimed that the variation in T. rex specimens was so great that they came from related species of giant carnivorous dinosaurs. However, this claim was based on a comparatively very small sample. When we compared data from hundreds of living birds, we found that T. rex was actually less variable than most theropod dinosaurs. This evidence for the proposed multiple species is not strong,” said James Napoli, one of the authors of the new study.
“Determining variation in long-extinct animals is a major challenge for paleontologists. Our study shows that rigorous statistical analysis based on what we know about living animals is the best way to clarify the boundaries of extinct species. Simply put, the three-species pattern is so poorly defined that many excellent specimens cannot be identified. This is a clear sign that the hypothesis is not applicable in the real world,” said another author of the new study, Thomas Carr of Carthage College.
“The boundaries of living species are very difficult to define. Zoologists, for example, disagree on the number of living species of giraffe,” added Thomas Holtz of the College of Maryland and the American Museum of Natural History.
“T. rex is an iconic species that is important both for paleontological research and for communicating science to the public, so it is important to have accurate information. There is still a possibility that there is another species of Tyrannosaurus, but we need strong evidence to make such a decision,” said David Hone of Queen Mary College of London.