NMMNHS News:

ALBUQUERQUE — A team of scientists studying fossils at the New Mexico Museum of Natural History & Science have identified a New Mexico fossil belonging to a surprisingly large and geologically old member of the lineage of dinosaurs that gave rise to the mighty Tyrannosaurus Rex.

This research, co-authored by New Mexico Museum of Natural History & Science (NMMNHS) Executive Director Dr. Anthony Fiorillo and NMMNHS curator Dr. Spencer Lucas, shows that large tyrannosaurs lived in what’s now New Mexico millions of years earlier than scientists realized. The finding brings researchers closer to understanding where and how these massive super-predators evolved. The research is published in Scientific Reports.

“This New Mexico discovery shifts the timeline for how some of the largest predators of all time evolved, and provides new insight on where they came from,” Dr. Fiorillo said. “Based on what we now know, it’s possible the ancestors of the most famous dinosaur of all evolved in what’s now New Mexico.”

“Moreover, both the body size and the geological age of this tyrannosaur discovery are confirmed by multiple sources of data,” Dr. Lucas said.

For as popular as T. rex is with dinosaur fans of all ages, its origins have long been a mystery. Various theories have put the origin of Tyrannosaurus in either Asia, where the related species Tarbosaurus is found in Mongolia, or in North America. However, evidence has emerged in recent years supporting a North American origin of very large tyrannosaurs. A large tyrannosaur vertebra was reported from the Big Bend region of Texas. Two years ago, a new Tyrannosaurus species, T. mcraeensis, was discovered in New Mexico, and while its precise age is somewhat uncertain it is clearly older than its more famous cousin, T. rex. This new discovery is another data point in favor of a North American origin.

The fossil in question, a shin bone collected years ago in the Bisti De-Na-Zin wilderness of New Mexico from a locality discovered by NMMNHS research associate Paul Sealey in 1997, was originally identified as a distinct species of tyrannosaur, Bistahieversor. Following the recent discovery of an early Tyrannosaurus species in New Mexico, the fossil was restudied and found to better match Tyrannosaurus. The large size – the animal weighed between four and five tons, larger than any tyrannosaur known from its time – and the shape of the ankle are a near-perfect match for T. rex.  

Using radioactive dating of the volcanic ash beds that bracket the bone, scientists were able to pinpoint its age between 74 and 75 million years ago, around 8 to 9 million years before T. rex roamed the earth. This suggests that a closely related ancestor may have roamed New Mexico during that time. Moreover, it provides support for the idea that the ancestors of T. rex evolved in the southern part of North America, perhaps in the American southwest or Mexico.

Dr. Nick Longrich, Senior Lecturer at the University of Bath and lead author on the study, noted that scientists can’t say with 100% certainty that this is an ancestor of T. rex until they find more bones, but evidence currently leans in that direction.

“Debate is how science proceeds,” said Dr. Nick Longrich, who led the study. “And by throwing this hypothesis out there, it will provoke debate and hopefully encourage people to take a closer look at museum collections and look for new material in the field. New fossils will support this hypothesis or reject it. Either way we’ll walk away with a better understanding of how the dinosaurs evolved.”

To learn more about NMMNHS’s Paleontology research, visit nmnaturalhistory.org/science/sections/paleontology. The museum will reopen to the public on Saturday, April 4.