Study refutes claim that T. rex was three separate species

A new study refutes a provocative claim made earlier this year. The rebuttal was published in the journal Evolutionary Biology and was led by paleontologists at the American Museum of Natural History.

Steve Brusatte, a paleontologist at the University of Edinburgh, said that tyrannosaurus rex is the true king of the dinosaurs. It was recently announced that T. rex was more than one species. In our new study, we show that the variation in size and shape of the fossils can't be neatly separated into clusters. T rex is the only giant predator from the end of the Age of Dinosaurs in North America.

The standard T. rex, the bulkier "T. imperator" and the slimmer "T. regina" should be reclassified as three species according to the authors of the study. The leg and teeth of 38 T. rex specimen were analyzed.

Data points from 112 species of living dinosaurs, as well as from four non-avian theropod dinosaurs, were added by the authors of the new study. The multiple species argument was based on a limited comparative sample.

The study claimed that the variation in T. rex specimen was so high that they were probably from multiple closely related species of giant meat-eating dinosaur. A very small sample was used to make this claim. We found that T. rex is less variable than other dinosaurs. The evidence doesn't hold up.

"Ping down variation in long extinct animals is a challenge for paleontologists," said co-lead author Thomas Carr. The best way to clarify the boundaries of extinct species is through rigorous statistical analyses that are based on our knowledge of animals. Many excellent specimen can't be identified by the three-species model. A hypothesis that doesn't map onto the real world is a warning sign.

The paper claimed that the size of the second tooth in the lower jaw indicated the presence of more than one species. The authors of the new study couldn't duplicate the tooth findings because they didn't have the same specimen. The authors of the new study didn't like how the breakpoints for each species were calculated. The authors of the new study said that the statistical analysis in the original study was not useful for testing the hypothesis. In the latest study, a different statistical technique was used to determine how many clusters exist within the data, and they found that they are best considered as a single group.

Zoologists don't agree on the number of living species of giraffe, according to co-author Thomas Holtz from the University of Maryland. The species involved are ancient and only known from a small number of samples. There are other sources of variation that have to be rejected before one accepts the idea that there are two different species. We don't think that hypothesis is the best explanation.

"T. rex is an important species 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. There is a chance that there is more than one species of tyrannosaurus, but we need strong evidence to make that decision.

More information: Thomas D. Carr, Insufficient Evidence for Multiple Species of Tyrannosaurus in the Latest 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", Evolutionary Biology (2022). DOI: 10.1007/s11692-022-09573-1. link.springer.com/article/10.1 … 7/s11692-022-09573-1

The Tyrant Lizard King, Queen and Emperor: Multiple Lines of Morphological and Stratigraphic Evidence supports Evolution and Probable Speciation within the North American Genus tyrannosaurus rex. It's called 10.1007/s11692 022-09561-5.

Journal information: Evolutionary Biology