As part of the museum’s temporary exhibit T. rex: The Ultimate Predator, on view from 2019 to 2021, visitors encountered a giant life-size model of a T. rex with feather spots – the most scientifically accurate depiction of T. rex that you can give. Photo credit: D. Finn/ ©AMNH
Paleontologists find insufficient evidence that the iconic Tyrannosaurus rex should be reclassified.
A bold claim made earlier this year that fossils have been identified as belonging to the dinosaur Tyrannosaurus rex really represent three different species is being debunked by new research. The rebuttal notes that the earlier proposal lacks enough evidence to split the iconic species. The study is published in the journal today (July 25, 2022). evolutionary biology and led by paleontologists from the American Museum of Natural History (AMNH) and Carthage College.
“Tyrannosaurus rex remains the one true king of dinosaurs,” said study co-author Steve Brusatte, a paleontologist at University of Edinburgh who completed his Ph.D. work in the museum. “Recently, with much fanfare, a bold theory was announced: what we call t rex was actually several types. It’s true that the fossils we have are somewhat variable in size and shape, but as we show in our new study, this variation is small and cannot be used to cleanly divide the fossils into easily defined clusters . Based on all the fossil evidence we currently have, t rex stands alone as the only giant apex predator from the end of the Dinosaur Age in North America.”
In March 2022, authors of the controversial study made that claim t rex should be reclassified into three types: the standard t rexthe more voluminousT. the Emperor,” and the slimmer “T.regina.” The study, which was also released in the diary evolutionary biologywas based on an analysis of the leg bones and teeth of 38 t rex specimens.
An illustration of a T. rex feeding. Photo credit: © Mark Witton 2022
In the new publication, the scientists reexamined the data presented in the earlier study and also added data points from 112 species of living dinosaurs — birds — and four non-avian theropod dinosaurs. They found that the multispecies argument was based on a limited comparative sample, incomparable measurements, and inappropriate statistical techniques.
“Their study claimed that the variation in t rex Specimens were so high that they likely came from several closely related species of giant carnivorous dinosaurs,” said James Napoli, co-lead author of the rebuttal study and a graduate doctoral student at the museum’s Richard Gilder Graduate School. “But that claim was based on a very small comparative sample In fact, comparing data from hundreds of live birds, we found that t rex is less variable than most living theropod dinosaurs. This line of evidence for proposed multiple species does not stand.”
“Tyrannosaurus rex remains the one true king of dinosaurs.” — Steve Brusatte
“Pinning down variations in long-extinct animals is a major challenge for paleontologists,” said co-lead author Thomas Carr of Carthage College. “Our study shows that rigorous statistical analysis based on our knowledge of living animals is the best way to clarify the boundaries of extinct species. In practice, the three species model is so poorly defined that many outstanding specimens cannot be identified. This is a clear warning sign of a hypothesis that does not correspond to the real world.”
Variations in the size of the second tooth in the mandible indicated the presence of multiple species according to the original work, in addition to the robustness of the femur. However, the authors of the new study were unable to replicate the dental findings, and they found different results from their own measurements on the same samples. Additionally, the new study’s scientists questioned how the “breaking points” were statistically determined for each species using these traits. Because the statistical analysis in the original study defined the number of groups before the test was administered, it is not useful for testing the hypothesis, according to the new study’s authors. In the latest paper, a different statistical technique was used to determine, without further assumptions, how many clusters exist in the data, finding that they are best viewed as a single group — in other words, a species —t rex.
“Even the boundaries of living species are very difficult to define: zoologists, for example, disagree on the number of living giraffe species,” said co-author Thomas Holtz of the University of Maryland and the National Museum of Natural History. “It becomes much more difficult when the species involved are old and only known from a relatively small number of specimens. Other sources of variation—changes with growth, with region, with sex, and with good old-fashioned individual differences—must be rejected before accepting the hypothesis that two groups of specimens are in fact different species. In our view, this hypothesis is not yet the best explanation.”
“t rex is an iconic species and incredibly important to both paleontological research and communicating with the public about science, so it’s important that we get this right,” said co-author David Hone of Queen Mary University of London. ” There is still a good chance that there is more than one species Tyrannosaurus out there, but we need strong evidence to make that kind of decision.”
References: “Insufficient evidence for several Tyrannosaurus species in recent times[{” attribute=””>Cretaceous of North America: A Comment on “The Tyrant Lizard King, Queen and Emperor: Multiple Lines of Morphological and Stratigraphic Evidence Support Subtle Evolution and Probable Speciation Within the North American Genus Tyrannosaurus”’ by Thomas D. Carr, James G. Napoli, Stephen L. Brusatte, Thomas R. Holtz Jr., David W. E. Hone, Thomas E. Williamson and Lindsay E. Zanno, 25 July 2022, Evolutionary Biology.
DOI: 10.1007/s11692-022-09573-1
