New research suggests the famous Tyrannosaurus rex originated in North America, not Asia. (Image credit: Jacobs Stock Photography Ltd/Getty Images)
New research has shown that the famous Tyrannosaurus rex may have evolved in a completely different place than its immediate predecessors.
The study builds on earlier work that suggested that T. rex’s ancestors arose in Asia and migrated to North America during a period of falling sea levels, creating a land bridge between the continents. The new study, published Wednesday (May 7) in the journal Royal Society Open Science, provides further evidence that T. rex originated in what is now North America — and that its direct ancestors, which have not yet been found, originated in Asia and migrated across the ancient land more than 70 million years ago.
T. rex lived between 67 and 66 million years ago, during the Late Cretaceous period, and could reach impressive sizes — up to 12.5 feet (3.8 meters) tall at the hips and up to 41 feet (12 meters) long. Most T. rex fossils have been found in the U.S. states of Montana and South Dakota, as well as Alberta, Canada — an area that was once an island continent known as Laramidia, stretching from parts of modern-day Alaska to Mexico.
T. rex evolved from smaller members of the tyrannosaurid family, and its origins have long been a subject of debate.
Because T. rex is more closely related anatomically to Asian tyrannosaur dinosaurs than to North American ones, a 2016 study found that T. rex's ancestors likely evolved in Asia and migrated to North America. The new study confirms that finding and suggests that T. rex then evolved in North America.
“The geographic origins of T. rex are hotly debated, with palaeontologists divided over whether its ancestor came from Asia or North America,” said lead author Cassius Morrison, a PhD student at University College London (UCL), in a commentary. “Our modelling suggests that T. rex’s ‘progenitors’ likely arrived in North America from Asia, crossing the Bering Strait between modern-day Siberia and Alaska.”
The researchers applied a model based on the locations and times of finds of different tyrannosaur species, their evolutionary trees, and climate conditions. They found that T. rex fossils are widespread in Laramidia, and the ancestor of T. rex existed in both Asia and Laramidia, indicating that the ancestor of T. rex likely migrated from Asia to North America between the late Campanian and early Maastrichtian, about 72 million years ago.
“This is consistent with previous studies that found that T. rex was more closely related to Asian relatives like Tarbosaurus than to North American relatives like Daspletosaurus,” Morrison said. “While dozens of T. rex fossils have been found in North America, our results suggest that fossils of a direct ancestor of T. rex may remain undiscovered in Asia.”
Steve Brusatte, a paleontologist at the University of Edinburgh and co-author of a 2016 study on the roots of Tyrannosaurus, called the new study “a remarkable piece of science.”
“T. rex was the quintessential American dinosaur: big, bold, ferocious, and the ruler of western North America during the last years of the Cretaceous,” Brusatte wrote in an email to Live Science. “But it was actually an immigrant. The most iconic American dinosaur was a migrant from Asia.”
Gigantic dimensions
The new study also modeled how tyrannosaurids (the group of dinosaurs to which
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