Unearthing the Truth: The Final Answer on T. Rex’s Controversial North American Origins

Paleontologists have different views on where the iconic Tyrannosaurus rex came from. Some argue it originated in North America, while others believe its ancestors traveled from Asia across the Bering Strait.

A recent study, led by paleoecologist Cassius Morrison from University College London, suggests that the roots of T. rex might actually trace back to Asia. Morrison states, “While many T. rex fossils are found in North America, we believe its direct ancestor fossils remain undiscovered in Asia.” This challenges previous ideas that linked T. rex more closely to North American relatives like Daspletosaurus rather than Asian ones such as Tarbosaurus.

In a 2024 report, scientists uncovered a fossil in New Mexico belonging to T. rex‘s relative Tyrannosaurus mcraeensis. This fossil, they claimed, predates T. rex by about 6 million years, suggesting large-bodied tyrannosaurs started in North America. However, Morrison’s team argues that based on the limited evidence, this conclusion may not hold true.

To better understand T. rex‘s family tree, Morrison’s group used advanced modeling techniques. They took into account the fossil record, dinosaur evolution, and the climate of the time. Their findings reveal how tyrannosaurs and their relatives, like megaraptors, navigated across continents.

Their models propose that although the T. rex genus likely emerged in the ancient landmass known as Laramidia, its direct ancestors probably migrated from Asia. Morrison emphasizes, “The Tyrannosaurus genus began in Laramidia from ancestors that crossed over from Asia during the Late Campanian to Early Maastrichtian.”

Interestingly, this theory isn’t entirely novel. Even smaller relatives of T. rex have left fossils that indicate migration across the Bering land bridge.

Looking at megaraptors, researchers found that they likely appeared in Asia around 120 million years ago before spreading to Europe and Africa. However, no megaraptor fossils have been located in Europe so far. Paleontologist Mauro Aranciaga Rolando notes that during the early Cretaceous, these predators were part of a diverse ecosystem. They eventually specialized based on their environment, with some becoming top predators in Australia and Patagonia as the continents drifted apart.

As the climate cooled around 92 million years ago, both megaraptors and tyrannosaurs grew to impressive sizes. But the study found no direct link between climate changes and this gigantism. Instead, it appears these dinosaurs adapted well to the colder conditions, stepping into an ecological role left vacant by extinct species.

UCL paleontologist Charlie Scherer explains, “They likely grew larger to replace giant carcharodontosaurid theropods that vanished around 90 million years ago. The extinction of these massive predators removed barriers, allowing tyrannosaurs to flourish.”

This research offers a fresh perspective on the lineage of T. rex and highlights ongoing debates in the paleontological community. For more insights, check out the research published in Royal Society Open Science.

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