T. Rex’s Asian Ancestry Revealed in Migration Study

A comprehensive new study published May 7, 2025, in Royal Society Open Science has solved a longstanding paleontological mystery about the origins of one of history’s most iconic predators. Researchers have discovered that while Tyrannosaurus rex evolved in North America, its direct ancestor likely crossed over from Asia more than 70 million years ago—a finding that reshapes our understanding of dinosaur evolution and ancient continental connections.

Tracing the King’s Family Tree

For decades, scientists have debated whether T. rex descended from North American ancestors or Asian relatives. The international research team, led by researchers from University College London, employed sophisticated biogeographical analysis to trace the evolutionary history of these fearsome predators.

“The geographic origin of T. rex is the subject of fierce debate. Palaeontologists have been divided over whether its ancestor came from Asia or North America,” said lead author Cassius Morrison, a PhD student at UCL Earth Sciences.

Their findings suggest T. rex’s “grandparents” likely migrated from Asia to North America via the Bering Land Bridge—the same route that later human populations would use to reach the Americas. This confirms earlier hypotheses that T. rex was more closely related to Asian cousins like Tarbosaurus than to North American relatives like Daspletosaurus.

Climate Connection to Dinosaur Gigantism

The study revealed another fascinating pattern: the evolution of giant body sizes in both tyrannosaurids and their cousins, the mysterious megaraptors, coincided with global cooling following the Cretaceous Thermal Maximum about 92 million years ago. This suggests these dinosaurs may have possessed adaptations that helped them thrive in cooler environments—potentially including feathers or more warm-blooded metabolisms.

Key findings from the research include:

• T. rex evolved in western North America (Laramidia) from Asian ancestors that crossed the Bering Land Bridge
• Megaraptoran dinosaurs were more widely distributed globally than previously thought
• Both tyrannosaurids and megaraptors grew to gigantic sizes at roughly the same time, following global cooling
• The extinction of other giant predators (carcharodontosaurids) around 90 million years ago created an ecological opportunity for these groups to evolve larger sizes

The Mysterious Megaraptors

While T. rex has dominated both scientific research and popular culture, the study also sheds light on the enigmatic megaraptors—equally fascinating predators that evolved a different hunting strategy with long arms and massive claws rather than the bone-crushing jaws of tyrannosaurs.

“At the beginning of their evolutionary history, around 120 million years ago, megaraptors were part of a widespread and diverse dinosaur fauna,” explained Dr. Mauro Aranciaga Rolando, from the Bernardino Rivadavia Natural Sciences Argentine Museum in Buenos Aires.

The research team concluded that megaraptors likely spread across much of the ancient supercontinent Gondwana, including regions where their fossils have yet to be discovered, such as Europe and Africa. This suggests these formidable predators were more diverse and widespread than previously recognized.

Hunting Different Prey in Different Places

One intriguing aspect of the study is how these two related groups of predators evolved different hunting strategies based on the prey available in their environments. In North America, T. rex likely hunted horned dinosaurs like Triceratops and duck-billed dinosaurs like Edmontosaurus. Meanwhile, in the southern continents, megaraptors may have specialized in hunting juvenile sauropods—the long-necked giants that dominated these ecosystems.

This geographical and ecological separation helped drive the evolution of their distinctive features: bone-crushing jaws for tyrannosaurs versus long arms with massive claws for megaraptors.

“Our findings have shined a light on how the largest tyrannosaurs appeared in North and South America during the Cretaceous and how and why they grew so large by the end of the age of dinosaurs,” said co-author Charlie Scherer, an Earth Sciences graduate and founder of UCL’s Palaeontology Society.

The study challenges previous findings that suggested T. rex evolved entirely within North America, arguing that recently discovered fossils of a purported T. rex relative in New Mexico (Tyrannosaurus mcraeensis) were not reliably dated. Instead, the evidence points to an Asian ancestor that migrated to North America and gave rise to the T. rex lineage.

As researchers continue to unearth new fossils and apply advanced analytical techniques, our understanding of dinosaur evolution continues to evolve—revealing a complex story of continental movements, climate changes, and ecological opportunities that shaped the incredible diversity of prehistoric life.