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Albuquerque, NM – A team of researchers that includes New Mexico Museum of Natural History & Science (NMMNHS) Executive Director Dr. Anthony Fiorillo authored a new study that reshapes our understanding of how the most famous dinosaur to ever walk the earth – Tyrannosaurus rex – first arrived in North America by introducing its earliest known relative on the continent.  

“This important discovery, made in New Mexico and co-authored by New Mexico researchers, demonstrates that our state remains at the forefront of scientific research and inquiry,” said Gov. Michelle Lujan Grisham. “New Mexico’s cultural institutions continue to lead the way on groundbreaking work in their respective fields and remain a key pillar of our statewide economy.” 

The study, published in the journal Scientific Reports, identifies a newly discovered subspecies of tyrannosaur known as Tyrannosaurus mcraeensis. The newly discovered predator is older and more primitive than its better-known cousin, but just as large. The study was based on a partial skull collected years ago from western New Mexico, currently on display at NMMNHS, which shows that Tyrannosaurus was in North America millions of years before paleontologists previously thought. 

“New Mexicans have always known our state is special, now we know that New Mexico has been a special place for tens of millions of years,” Dr. Fiorillo said. “This study delivers on the mission of this museum through the science-based investigation of the history of life on our planet.” 

Alongside NMMNHS, authors on the study include researchers from the University of Bath (UK), University of Utah, The George Washington University, Harrisburg University, Penn State Lehigh Valley, and the University of Alberta. 

Tyrannosaurus rex, perhaps the largest and most dangerous terrestrial predator of all time, suddenly appeared in North America around 66 million years ago. But with no close relatives in North America, how it arrived and evolved on the continent remains a mystery. When then-student Sebastian Dalman began a restudy of a horned dinosaur from the same fauna, it forced a broader rethink of the dinosaurs from western New Mexico. “I started working on this project in 2013 with co-author Steve Jasinski and soon we started to suspect we were on to sometime new,” Dalman said. 

A team of scientists from New Mexico; Pennsylvania; Washington DC; Utah; Ontario, Canada; and Bath, United Kingdom was assembled to study the animal, going through the skeleton bone by bone. In each case, they found subtle differences between the specimen and the dozens of T. rex skeletons that had been found before. Because T. rex is so well-known, it became possible to show the New Mexico tyrannosaur was something new.   

“The differences are subtle, but that’s typically the case in closely related species. Evolution slowly causes mutations to build up over millions of years, causing species to look subtly different over time,” said Dr. Nick Longrich, a co-author from the Milner Centre for Evolution at the University of Bath (UK). 

The newly discovered Tyrannosaurus mcraeensis was roughly the same size as a T. rex, which measured up to 40 feet long and 12 feet high. Like its famous relative, Tyrannosaurus ate meat. While the new discovery predates T. Rex, the paper notes that subtle differences in the jaw bones make it unlikely that it was a direct ancestor. This raises the possibility that there are still more new tyrannosaur discoveries to be made. 

“Once again, the extent and scientific importance of New Mexico’s dinosaur fossils becomes clear—many new dinosaurs remain to be discovered in the state, both in the rocks and in museum drawers!” said Dr. Spencer Lucas, Paleontology Curator at NMMNHS. 

The new discovery expands our understanding of tyrannosaurs in several ways. First, they suggest that the apex predators lived in what’s now the southern United States at least 72 million years ago, long before the first fossils of T. Rex were found in the same region. Tyrannosaurus likely originated in southern North America then later expanded into much of the western portion of the continent. 

The new fossils also suggest that larger, more heavily built, and more advanced species evolved in the southern United States, compared to the smaller and more primitive tyrannosaurs that inhabited Montana and Canada. For reasons that remain to be discovered, dinosaurs may have evolved to larger sizes in the south, a body size pattern opposite the pattern seen in modern mammals. Then, towards the very end of the Cretaceous Period, for reasons unknown, the giant tyrannosaurs suddenly spread north, alongside giant horned dinosaurs like Triceratops and Torosaurus. It may be that the northern spread of the giant horned dinosaurs created a food source that could support giant tyrannosaurs.   

These fossils were collected on lands administered by the U.S. Bureau of Reclamation. The partial skull of the Tyrannosaurus mcraeensis is on view at the New Mexico Museum of Natural History & Science. To learn more, visit nmnaturalhistory.org. 

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.