A recent study proffered the idea that Tyrannosaurus rex, arguably the most famous of the dinosaurs, may have been three species instead of one. While names like Tyrant Lizard Emperor and Tyrant Lizard Queen made the prospect a spicy one, a new paper refutes the findings in saying that there’s insufficient evidence to justify splitting the species (at least, for now).
“Tyrannosaurus rex remains the one true king of the dinosaurs,” study co-author Steve Brusatte, a palaeontologist at the University of Edinburgh whose recent scientific contributions include consulting on Jurassic World Dominion and describing the largest ever pterosaur, said in a statement.
“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.”
Published to Evolutionary Biology, Brusatte joins a body of voices from the palaeontological community who expressed doubts over the proposed split when the original paper was published. To bolster their argument, the researchers on the new paper revisited the data and included further information on 112 species of living dinosaurs – birds – as well as four non-avian theropod dinosaurs
“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 American Museum of Natural History'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.”
While it might seem strange for so much debate to exist around evidence for and against species, identifying unique individuals among groups of closely-related animals is something we struggle with even in those alive today.
“The boundaries of even living species are very hard to define: for instance, zoologists disagree over the number of living species of giraffe,” said co-author Thomas Holtz, from the University of Maryland and the National Museum of Natural History. “It becomes much more difficult when the species involved are ancient and only known from a fairly small number of specimens.”
While the researchers on this new paper conclude that there is insufficient evidence to support a trio of T. rex species, they’re not saying that it was definitely just a single animal, either. It could be that future, more robust evidence could tip the academic scale in favor of several species of T. rex, but we’re not there yet.
“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 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.”