Is the mighty tyrannosaurus rex really three species of dinosaurs, as a study earlier this year claimed? Fuggedaboutit, according to a new study.
The rebuttal, published online today (July 25) in the journal evolutionary biology (opens in a new tab)shows that the T. rex “trio” study lacks the weight evidence to support its ideas.
“tyrannosaurus rex remains the only true king of dinosaurs“said study co-author Steve Brusatte, a paleontologist at the University of Edinburgh in Scotland, in a statement released today by the American Museum of Natural History (AMNH) in New York.
However, the lead author of the original study, Gregory Paul, an independent paleontologist, is not convinced by the new findings. “[It] is not a real scientific study,” Paul told Live Science in an email. “It comes across as paleopropaganda that appears to be structured to defend T. rexrather than seriously exploring the possibilities that fossil specimens of the genus Tyrannosaurus contained more than one species than the genus certainly contained.”
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The controversial study by Paul and his co-authors, published in March 2022, also in the journal evolutionary biology (opens in a new tab)proposed that T. rex was three distinct species, which have been identified as the standard T. rexthe bulkiest T.imperatorand the thinnest T. Regina. The authors based their conclusions on an analysis of the femurs (thigh bones) and teeth of 38 T. rex people.
However, their study was pushed back before it was even published. The authors did not definitively assign a species to each specimen they analyzed, even those with well-preserved remains. As a result, Philip Currie, a well-known paleontologist from the University of Alberta in Canada, removed his name from the study before its release, The New York Times reported at the time.
Despite this controversy, Paul, who does not have a degree in the field but has contributed to a large amount of published studies, defended the article. “I’m aware there might be a lot of people out there who aren’t going to be happy about this,” Paul previously told The New York Times. “And my answer is: publish a rebuttal.”
Now, a group of researchers with expertise in theropods – a group of bipedal, largely carnivorous dinosaurs that included T. rex and his close relatives – did just that.
“Recently, a bold theory was announced with great fanfare: what we call T. rex was actually several species,” Brusatte said in the statement. “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 does not cannot be used to neatly separate fossils into easily definable clusters. Based on all the fossil evidence we currently have, T. rex is the only giant predator from the end of the age of dinosaurs in North America.”
In the new study, the researchers looked at data from the March study, in addition to data points from 112 species of birds – which are living dinosaurs – and four non-avian theropods, including Tarbosaurus bataar and Albertosaurus sarcophagus. Their analysis revealed that the “three species” proposal was based on a limited comparative sample, non-comparable measurements and inappropriate statistical techniques, according to the AMNH statement.
“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,” study co-lead author James Napoli, a graduate doctoral student at AMNH’s Richard Gilder Graduate School, said. assertion was based on a very small number of specimens. 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.”
Related: Are birds dinosaurs?
Pinpointing species-defining variation in long-extinct animals can be difficult, said study co-lead author Thomas Carr, a vertebrate paleontologist and associate professor of biology at Carthage College in Wisconsin. That’s why the authors of the new study looked at living dinosaurs, as well as extinct ones.
“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,” Carr said in the statement. “In practical terms, the three-species model is so poorly defined that many excellent specimens cannot be identified. This is a clear warning sign of a hypothesis that does not correspond to the real world.”
The March study suggested that when researchers looked at several T. rex specimens, variations in size in the second tooth of the lower jaw and in the sturdiness of the femur, revealed that the iconic dinosaur was, in fact, three species. However, researchers in the new study could not replicate the finding of the tooth. They even got different results on simple measurements of the dental samples.
Additionally, the researchers of the new study disagreed with how the original paper statistically determined the three species. In the original study, the statistical analysis defined the three groups before the test was actually run, so it could not blindly test the ‘trio’ hypothesis, the new study authors said. . In the new study, the researchers used a different statistical technique to see how many clusters existed in the data without any prior assumptions. Their results showed that T. rex is best considered as a single group, i.e. as a single species.
“Species boundaries, even living ones, are very difficult to define: for example, zoologists disagree on how many living species of giraffe there are,” said study co-author Thomas Holtz. , a vertebrate paleontologist at the University of Maryland and the Smithsonian National Museum of Natural History in Washington, DC, said in the statement. “It becomes much more difficult when the species involved are old and only known from a fairly small number of specimens. Other sources of variation – changes with growth, with region, with sex and with good differences old-fashioned individual – must be rejected before accepting the hypothesis that two sets of specimens are in fact distinct species.In our opinion, this hypothesis is not yet the best explanation.
But Paul disagreed with the assessment of the new study, calling it “a very flawed work that does not refute the data and analysis presented by Paul et al. (2022), and has its own errors. “Paul told Live Science in an email in which he included a long list of disagreements he had with the new publication.
Paul also disputed that the original study “took a dozen years to produce”, while the new study “was produced in weeks, reviewed and published in just months and the adverse results show it” .
T. rex is famous in the dinosaur world and in popular culture, “so it’s important that we get it right,” said new study co-author David Hone, senior lecturer in zoology at the University. Queen Mary 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. »
Originally posted on Live Science.