As part of the Museum’s temporary exhibition T. rex: The Ultimate Predator, which was on display from 2019-2021, visitors encountered a huge life-size 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 statement made earlier this year fossils identified as belonging to the dinosaur tyrannosaurus rex actually represent three distinct species is discredited by new research. The rebuttal finds that the previous proposal lacks sufficient evidence to split the iconic species. The study is published today (July 25, 2022) in the journal evolutionary biology and run by paleontologists at the American Museum of Natural History (AMNH) and Carthage College.
“tyrannosaurus rex remains the only true king of the dinosaurs,” said study co-author Steve Brusatte, a paleontologist at the University of Edinburgh who did his Ph.D. I work at the Museum. “Recently, a bold theory was announced with great fanfare: what we call tyrannosaurus rex it was actually multiple species. It’s true that the fossils we do 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 clearly separate fossils into easily defined groups. Based on all the fossil evidence we currently have, tyrannosaurus rex stands alone as the only giant apex predator from the end of the Age of Dinosaurs in North America.”
In March 2022, the authors of the controversial study argued that tyrannosaurus rex should be reclassified into three species: the standard tyrannosaurus rexthe bulkiestT imperatorand the thinnestT.regina.” The study, which was also published In the diary evolutionary biologywas based on an analysis of the leg bones and teeth of 38 tyrannosaurus rex specimens
An illustration of a T. rex feeding. Credit: © Mark Witton 2022
In the new paper, the scientists revised the data presented in the previous 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 inadequate statistical techniques.
“Their study asserted that the variation in tyrannosaurus rex specimens was so tall that they were likely from multiple 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 this claim was based on a very small comparative sample. Compared to data from hundreds of live birds, we actually found that tyrannosaurus rex it is less variable than most living theropod dinosaurs. This line of evidence for the multiple proposed species does not hold up.”
“tyrannosaurus rex remains the only true king of the dinosaurs.” — steve brusatte
“Pinpointing variation in long-extinct animals is a huge challenge for paleontologists,” said co-senior author Thomas Carr of Carthage College. “Our study shows that rigorous statistical analyzes that build on 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 not many excellent specimens can be identified. That is a clear warning sign of a hypothesis that does not correspond to the real world.”
The variation in the size of the second tooth in the lower jaw, in addition to the robustness of the femur, indicated the presence of multiple species according to the original article. However, the authors of the new study were unable to replicate the dental findings and retrieved different results from their own measurements of the same samples. In addition, the scientists in the new study addressed the issue of how “cutoff points” were statistically determined for each species that uses these traits. Because the statistical analysis in the original study defined the number of groups before running the test, it is not useful for testing the hypothesis, according to the authors of the new study. In the last article, a different statistical technique was used to determine how many groups exist within the data without advanced assumptions, and it was found that they are best considered as a single group, in other words, a species.tyrannosaurus rex.
“Even living species boundaries are very difficult to define: for example, zoologists disagree about the number of living species of giraffes,” said co-author Thomas Holtz, of the University of Maryland and the National Museum of History. Natural. “It becomes much more difficult when the species involved are ancient and only known from a fairly small number of specimens. Other sources of variation—changes with growth, with region, with sex, and with good old-fashioned individual differences—have to be rejected before accepting the hypothesis that two sets of specimens are in fact separate species. In our opinion, that hypothesis is still not the best explanation.”
“tyrannosaurus rex it’s an iconic species and incredibly important for both paleontological research and communicating science to the public, so it’s important we get it 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 solid evidence to make that kind of decision.”
Reference: ‘Insufficient evidence for multiple species of Tyrannosaurus in recent[{” 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
