A new fossil discovery highlights the closest known relative of the dinosaur Tyrannosaurus rex

Reconstruction of Tyrannosaurus macrinsis. Credit: Sergei Krasinski, Editing

A re-examination of fossils collected in New Mexico unearths key clues about the origins of T. rex in North America.

A new study published in Scientific reports It reshapes our understanding of how the most famous dinosaurs ever walked on Earth – Tyrannosaurus rex -It first arrived in North America by introducing its closest known relative on the continent.

The study identifies a newly discovered subspecies of the dinosaur known as Tyrannosaurus macrinsis. The newly discovered predator is older and more primitive than its better-known cousin, but is the same size – about the size of a double-decker bus.

Discovery from New Mexico

The study was based on a partial skull collected years ago from western New Mexico, currently on display at the New Mexico Museum of Natural History and Science (NMMNHS), which shows that the dinosaur existed in North America millions of years earlier than paleontologists previously thought.

Contributing authors to the study include researchers from the University of Bath (UK), NMMNHS, the University of Utah, George Washington University, the University of Harrisburg, Pennsylvania State University Lehigh Valley, and the University of Alberta.

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

Teeth of Tyrannosaurus macrinsis. Credit: Nick Longrich

Rethinking the T. rex's evolutionary journey

Tyrannosaurus rex, perhaps the largest and most dangerous terrestrial predator ever, suddenly appeared in North America about 66 million years ago. But with no relatives in North America, how it arrived and evolved on the continent remains a mystery.

When Sebastian Dahlmann, a student at the time, began re-studying a horned dinosaur from the same fauna, it forced a broader rethink of dinosaurs from western New Mexico.

“I started working on this project in 2013 with co-author Steve Jasinski and quickly began to suspect that we were headed toward something new,” Dallman said.

Uncover subtle differences

A team of scientists from Bath (UK), USA and Canada was assembled to study the animal, examining the skeleton bone by bone. In each case, they found subtle differences between the sample and dozens of them T-Rex Skeletons that have been found before.

because T-Rex It has become possible to prove that the New Mexico tyrannosaur was something new.

“The differences are subtle, but this is usually the case in close association Classify. Dr Nick Longrich, co-author from the Milner Center for Evolution at the University of Bath, said evolution slowly causes mutations to accumulate over millions of years, making species look very different over time.

Tyrannosaurus macrinsis jaw at the New Mexico Museum of Natural History and Science. Note the large scar on the back of the jaw, which the authors speculate may have been caused by a fight with another tyrannosaur. Credit: Nick Longrich

Tyrannosaurus macrinsis: new type

Newly discovered Tyrannosaurus macrinsis It was almost the same size as A T-RexWhich reaches 40 feet (12 m) in length and 12 feet (3.6 m) in height. Like his famous relative Tyrannosaurus macrinsis eating meat. While the new discovery precedes T-RexThe paper suggests that subtle differences in the jaw bones make it unlikely to be a direct ancestor.

This raises the possibility that there are still more new dinosaur 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 rocks and in museum drawers!” said Dr. Spencer Lucas, Curator of Paleontology at NMMNHS.

Expanding our understanding of tyrannosaurs

The new discovery expands our understanding of tyrannosaurs in several ways. First, they suggest that predators lived in what is now the southern United States at least 72 million years ago, long before the first fossils of living organisms were discovered. T-Rex They were found in the same area.

The dinosaur likely originated in southern North America and later expanded into much of the western part of the continent.

The new fossils, collected on lands managed by the US Bureau of Reclamation, also indicate that larger, denser and more advanced species evolved in the southern United States, compared to the smaller, more primitive tyrannosaurs that inhabited Montana and Canada. .

Kettle Top Butte in southeastern New Mexico. This fossilized jaw of Tyrannosaurus mcraeensis was discovered near the base of the buttstock. Image source: Dr. Spencer Lucas, New Mexico Museum of Natural History and Science. NM Credit Department for Cultural Affairs

Conclusion: Revealing the evolution of dinosaurs

For reasons yet to be discovered, dinosaurs may have evolved to larger sizes in the south, a pattern in body size that contradicts the pattern seen in modern mammals.

Then, eventually Cretaceous period For unknown reasons, giant dinosaurs suddenly spread northward, along with giant horned dinosaurs such as Triceratops and Torosaurus. The northern spread of giant horned dinosaurs likely created a food source that could support the giant dinosaurs.

It seems that more than a century after the dinosaur was first discovered, there is still a lot we don't know yet.

Reference: “A Giant Tyrannosaurus of the Campanian-Maastrian Period of Southern North America and the Evolution of Tyrannosaurus Gigantism” by Sebastian J. Dalman, Mark A. Lewin, R. Alexander Perron, Stephen E. Jasinski, D. Edward Malinczak, Spencer J. Lucas, Anthony R. Fiorello, Philip J. Currie, and Nicholas R. Longrich, January 11, 2024, Scientific reports.
doi: 10.1038/s41598-023-47011-0