Archaeologists re-examining fossils collected in New Mexico have uncovered key clues to the origins of Tyrannosaurus rex in North America. A new study published in Scientific Reports reshapes our understanding of how the most famous dinosaur to ever walk the earth, Tyrannosaurus rex, first came to North America by introducing its earliest relatives on the continent.
The study identifies a newly discovered subspecies of Tyrannosaurus rex - Tyrannosaurus mcraeensis. This newly discovered predator is older and more primitive than its well-known cousin, but just as massive -- about the size of a double-decker bus.
The research is based on a partial skull collected years ago from western New Mexico that is currently on display at the New Mexico Museum of Natural History and Science (NMMNHS).
Authors involved in the study include researchers from the University of Bath in the UK, NMMNHS, the University of Utah, George Washington University, Harrisburg University, Penn State Lehigh Valley and the University of Alberta.
"New Mexico people 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. Fiorillo, executive director of the New Mexico Institute of Natural and Human Sciences. "This research fulfills the museum's mission through the scientific investigation of the history of life on Earth."
Reflecting on the evolution of Tyrannosaurus rex
Tyrannosaurus rex, possibly the largest and most dangerous land predator ever, suddenly appeared in North America about 66 million years ago. However, how it came to the continent and evolved remains a mystery as it has no close relatives in North America.
When then-student Sebastian Dalman began re-examining ceratopsians from the same group of animals, it forced him to rethink the dinosaurs of western New Mexico more broadly.
"I started working on this project with co-author Steve Jasinski in 2013, and we quickly began to suspect that we had discovered a new continent," Dahlman said.
A team of scientists from Bath, UK, the US and Canada studied the animal's skeleton bone by bone. In each case, they found subtle differences between the specimens and dozens of previously discovered T. rex skeletons.
Because T. rex is so well-known, it might be possible to prove that the New Mexico T. rex is a new creature.
"The differences are subtle, but typical of closely related species," said co-author Dr. Nick Longrich of the Milner Center for Evolution at the University of Bath. "Evolution slowly leads to the accumulation of mutations over millions of years, making species subtly different over time."
a new species
The newly discovered McRae is about the same size as Tyrannosaurus rex, which was 40 feet (12 meters) long and 12 feet (3.6 meters) tall. Like its close relative the Tyrannosaurus rex, the McCree's Tyrannosaurus rex ate meat. Although the newly discovered T. rex predates T. rex, the paper notes that it is unlikely to be a direct ancestor of T. rex due to subtle differences in its jawbones.
This raises the possibility that there are many more new T. rexes waiting to be discovered.
Dr. Spencer Lucas, Curator of the New Mexico Museum of Paleontology, said, "Once again, the range and scientific importance of New Mexico's dinosaur fossils have become clear - there are still many new dinosaurs to be discovered in the state, whether in the rocks or in museum drawers!"
The new discovery expands our understanding of Tyrannosaurus rex in several ways. First, the findings suggest that this apex predator lived in what is now the southern United States at least 72 million years ago, much earlier than the first T. rex fossils were discovered in the same area.
Tyrannosaurus rex likely originated in southern North America and later expanded to much of the western part of the continent.
The new fossils, collected on land managed by the U.S. Bureau of Reclamation, also show that a larger, more massive and more advanced species evolved in the southern United States than the smaller, more primitive T. rex that inhabited Montana and Canada.
Conclusion: Uncovering the Mysteries of Dinosaur Evolution
For reasons that have yet to be discovered, dinosaurs may have evolved to larger sizes in the south, a body size pattern that is opposite to that of modern mammals.
Then, at the end of the Cretaceous, for unknown reasons, the giant Tyrannosaurus rex suddenly spread northward, and at the same time, giant horned dinosaurs such as Triceratops and Salamander also spread northward. It may be that Megaceratops' northward migration provided a food source for the giant Tyrannosaurus rex.
More than a century after Tyrannosaurus rex was first discovered, it seems there's still a lot we don't understand.