“Bold theory” that T. rex was disproved by 3 species – “Tyrannosaurus rex remains the only true king of the dinosaurs”

As part of the Museum’s temporary exhibition T. rex: The Ultimate Predator, which ran from 2019 to 2021, visitors encountered a huge life-size model of T. rex with patches of feathers – the most most scientifically accurate of T. rex to date. Credit: D. Finnin/ ©AMNH

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

A bold claim 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 concludes that the earlier proposal lacks sufficient evidence to split the emblematic species. The study is published today (July 25, 2022) in the journal evolutionary biology and led by paleontologists from 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 conducted his PhD. work at the museum. “Recently, a bold theory was announced with great fanfare: what we call T. rex was actually several species. It is true that the fossils we have are somewhat variable in size and shape, but as we show in our new study, this variation is minor and cannot be used to cleanly separate the fossils into easily defined clusters. Based on all the fossil evidence we currently have, T. rex is the only giant predator of the late dinosaur era in North America. »

In March 2022, the authors of the controversial study argued that T. rex should be reclassified into three species: the standard T. rexthe bulkiest”T.imperator“, and the thinnest”T. Regina.” The study, also published in the journal evolutionary biologywas based on an analysis of the leg bones and teeth of 38 T. rex specimens.

tyrannosaurus rex

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

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

“Their study affirmed that the variation of T. rex specimens were so high that they likely came from several closely related species of giant meat-eating 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. 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 the proposed multiple species does not hold water.

tyrannosaurus rex remains the only true king of the dinosaurs. — Steve Brusatte

“Identifying 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 analyzes based on our knowledge of living animals are the best way to clarify the boundaries of extinct species. In practical terms, the three-species pattern is so poorly defined that many excellent specimens cannot be identified. It is a clear warning sign of an assumption that does not correspond to the real world.

The variation in the size of the second tooth of the lower jaw, in addition to the sturdiness of the femur, indicated the presence of several species according to the original article. However, the authors of the new study could not reproduce the results of the teeth and they retrieved different results from their own measurements of the same specimens. Additionally, the scientists in the new study took issue with how the “breakpoints” for each species using these traits were statistically determined. Since the statistical analysis of the original study defined the number of groups before the test was run, it is not useful for testing the hypothesis, according to the authors of the new study. In the last paper, a different statistical technique was used to determine how many groups exist in the data without any assumptions being made, finding that they are best considered as a single group – in other words, a species –T. rex.

“Species boundaries, even living ones, are very difficult to define: for example, zoologists disagree on how many living species of giraffe there are,” 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 concerned are old and are 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 discarded before accepting the hypothesis that two sets of specimens are in fact species. distinct. In our opinion, this hypothesis is not yet the best explanation.

T. rex is an iconic and hugely important species for paleontological research and communicating science to the public, so it’s important that 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 several tyrannosaur species 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

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