New Fossil Discovery Sheds Mild on Tyrannosaurus Rex’s Earliest Recognized Relative

Restudy of fossils collected in New Mexico digs up key clues about T. rex’s origins in North America.

A brand new research printed in Scientific Studies reshapes our understanding of how probably the most well-known dinosaur to ever stroll the earth – Tyrannosaurus rex – first arrived in North America by introducing its earliest recognized relative on the continent.

The research identifies a newly found subspecies of tyrannosaur often known as Tyrannosaurus mcraeensis. The newly found predator is older and extra primitive than its better-known cousin, however simply as giant – roughly the scale of a double-decker bus.

Discovery From New Mexico

The research was primarily based on a partial cranium collected years in the past from western New Mexico, at present on show on the New Mexico Museum of Pure Historical past & Science (NMMNHS), which exhibits that Tyrannosaurus was in North America tens of millions of years earlier than paleontologists beforehand thought.

Contributing authors on the research embody researchers from the College of Bathtub (UK), NMMNHS, College of Utah, The George Washington College, Harrisburg College, Penn State Lehigh Valley, and the College of Alberta.

“New Mexicans have all the time recognized our state is particular, now we all know that New Mexico has been a particular place for tens of tens of millions of years,” Dr. Fiorillo, Government Director of NMMNHS mentioned. “This research delivers on the mission of this museum via the science-based investigation of the historical past of life on our planet.”

Enamel of Tyrannosaurus mcraeensis. Credit score: Nick Longrich

Rethinking T. rex’s Evolutionary Journey

Tyrannosaurus rex, maybe the biggest and most harmful terrestrial predator of all time, all of the sudden appeared in North America round 66 million years in the past. However with no shut kinfolk in North America, the way it arrived and advanced on the continent stays a thriller.

When then-student Sebastian Dalman started a restudy of a horned dinosaur from the identical fauna, it pressured a broader rethink of the dinosaurs from western New Mexico.

“I began engaged on this mission in 2013 with co-author Steve Jasinski and shortly we began to suspect we had been on to one thing new,” Dalman mentioned.

Uncovering Delicate Variations

A staff of scientists from Bathtub (UK), USA and Canada was assembled to review the animal, going via the skeleton bone by bone. In every case, they discovered refined variations between the specimen and the handfuls of T. rex skeletons that had been discovered earlier than.

As a result of T. rex is so well-known, it grew to become potential to point out the New Mexico tyrannosaur was one thing new.

“The variations are refined, however that’s sometimes the case in carefully associated species. Evolution slowly causes mutations to construct up over tens of millions of years, inflicting species to look subtly completely different over time,” mentioned Dr. Nick Longrich, a co-author from the Milner Centre for Evolution on the College of Bathtub.

Jaw of Tyrannosaurus mcraeensis on the New Mexico Museum of Pure Historical past and Science. Notice the massive scar in direction of the again of the jaw, which the authors speculate could have resulted from a struggle with one other Tyrannosaurus. Credit score: Nick Longrich

Tyrannosaurus mcraeensis: A New Species

The newly found Tyrannosaurus mcraeensis was roughly the identical measurement as a T. rex, which measured as much as 40 toes (12 meters) lengthy and 12 toes (3.6 meters) excessive. Like its well-known relative, Tyrannosaurus mcraeensis ate meat. Whereas the brand new discovery predates T. rex, the paper notes that refined variations within the jaw bones make it unlikely that it was a direct ancestor.

This raises the likelihood that there are nonetheless extra new tyrannosaur discoveries to be made.

“As soon as once more, the extent and scientific significance of New Mexico’s dinosaur fossils turns into clear—many new dinosaurs stay to be found within the state, each within the rocks and in museum drawers!” mentioned Dr. Spencer Lucas, Paleontology Curator at NMMNHS.

Increasing Our Understanding of Tyrannosaurs

The brand new discovery expands our understanding of tyrannosaurs in a number of methods. First, they counsel that the apex predators lived in what’s now the southern United States at the least 72 million years in the past, lengthy earlier than the primary fossils of T. Rex had been present in the identical area.

Tyrannosaurus possible originated in southern North America then later expanded into a lot of the western portion of the continent.

The brand new fossils, which had been collected on lands administered by the U.S. Bureau of Reclamation, additionally counsel that bigger, extra closely constructed, and extra superior species advanced within the southern United States, in comparison with the smaller and extra primitive tyrannosaurs that inhabited Montana and Canada.

Kettle High Butte in southeastern New Mexico. This fossilized jaw from Tyrannosaurus mcraeensis was uncovered close to the bottom of the butte. Credit score: Dr. Spencer Lucas, NM Museum of Pure Historical past & Science. Credit score NM Division of Cultural Affairs

Conclusion: Unraveling Dinosaur Evolution

For causes that stay to be found, dinosaurs could have advanced to bigger sizes within the south, a physique measurement sample reverse the sample seen in fashionable mammals.

Then, in direction of the very finish of the Cretaceous Interval, for causes unknown, the enormous tyrannosaurs all of the sudden unfold north, alongside big horned dinosaurs like Triceratops and Torosaurus. It could be that the northern unfold of the enormous horned dinosaurs created a meals supply that would assist big tyrannosaurs.

It appears greater than a century after Tyrannosaurus was first found, there’s loads we nonetheless don’t know.

Reference: “An enormous tyrannosaur from the Campanian–Maastrichtian of southern North America and the evolution of tyrannosaurid gigantism” by Sebastian G. Dalman, Mark A. Loewen, R. Alexander Pyron, Steven E. Jasinski, D. Edward Malinzak, Spencer G. Lucas, Anthony R. Fiorillo, Philip J. Currie and Nicholas R. Longrich, 11 January 2024, Scientific Studies.
DOI: 10.1038/s41598-023-47011-0