Releases | New Mexico Department of Cultural Affairs

The one true king

August 4th, 2022

Albuquerque, NM - The mighty Tyrannosaurus rex should continue to be classified as a single unique species, according to a new report co-authored by a researcher from the New Mexico Museum of Natural History & Science (NMMNHS).  

The new paper, published recently in the journal Evolutionary Biology and headed by paleontologists at the American Museum of Natural History and Carthage College, refutes a provocative claim made earlier this year that fossils classified as the iconic dinosaur T. rex represent three separate species. The new study finds that the earlier proposal lacks sufficient evidence to split up the iconic species.   

“There appears to be only one species of the ‘Tyrant Lizards’, and that’s the king, T. rex,” said Dr. Thomas Williamson, paleontology curator for NMMNHS and co-author of the study. 

In March 2022, authors of a controversial study, also published in Evolutionary Biology, made the case that T. rex should be reclassified as three species: the standard T. rex, the bulkier “T. imperator,” and the slimmer “T. regina.” The study was based on analysis of the leg bones and teeth of 38 T. rex specimens.  

The authors of the new study revisited the data presented in the earlier paper and added data points from 112 species of living dinosaurs — birds — and from four non-avian theropod dinosaurs. They found that the multiple species argument was based on a limited comparative sample, non-comparable measurements, and improper statistical techniques. 

“When compared to data from hundreds of living birds, we actually found that T. rex is less variable than most living theropod dinosaurs, said James Napoli, co-lead author of the new study and a graduating doctoral student in the Museum’s Richard Gilder Graduate School. “This line of evidence for proposed multiple species doesn’t hold up.” 

Dr. Williamson at NMMNHS applied his extensive body of research on tyrannosaurs to the study. He previously collected Bistahieversor sealeyi (a.k.a., “The Bisti Beast”), an earlier cousin of T. rex, from the San Juan Basin of northern New Mexico in the late 1990s.  

He later teamed up with Dr. Thomas Carr of Carthage College to describe and name the dinosaur and two additional tyrannosaur genera and species. In their research, Dr. Carr and Dr. Williamson examined many specimens of Tyrannosaurus and other tyrannosaurs housed in major museums in the U.S. and Canada, placing them among North America’s top tyrannosaur experts. 

About the New Mexico Museum of Natural History and Science The New Mexico Museum of Natural History and Science is a division of the Department of Cultural Affairs, under the leadership of the Board of Trustees of the New Mexico Museum of Natural History & Science. Programs and exhibits are generously supported by the New Mexico Museum of Natural History Foundation, through the generous support of donors. Established in 1986, the mission of the New Mexico Museum of Natural History & Science is to preserve and interpret the distinctive natural and scientific heritage of our state through extraordinary collections, research, exhibits, and programs designed to ignite a passion for lifelong learning. The NMMNHS offers exhibitions, programs, and workshops in Geoscience, including Paleontology and Mineralogy, Bioscience, and Space Science. It is the Southwest’s largest repository for fossils and includes a Planetarium and a large format 3D DynaTheater. 

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Bisti Beast Skull, Courtesy of NM Museum of Natural History & Science.

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