It has loomed in museums, rampaged through box offices, and haunted the imaginations of generations. From “Jurassic Park” to planetarium exhibits, Tyrannosaurus rex has come to symbolize prehistoric North America. But a new scientific study suggests the most iconic predator of the Late Cretaceous may not have been a native of the continent after all.
According to a peer-reviewed paper published in Royal Society Open Science in May 2025, a multinational team of paleontologists led by Cassius Morrison at the University of Bath has uncovered compelling evidence that the direct ancestors of T. rex evolved in Asia and migrated into western North America over 70 million years ago. The research draws on fossil data, evolutionary trees, and advanced biogeographic modeling, a method that uses mathematical simulations to reconstruct ancient species movement, to trace how the massive predator’s lineage may have crossed into North America via the prehistoric land bridge that once connected Siberia and Alaska.
“Our results support the hypothesis that large-bodied tyrannosaurines originated in Asia and dispersed into western North America during the Late Cretaceous,” Morrison and his coauthors wrote.
A Long Way From Home
For more than a century, Tyrannosaurus rex has been known only from fossils found in North America, particularly in Montana, Wyoming, and the Dakotas. First described by paleontologist Henry Fairfield Osborn in 1905, T. rex quickly became a symbol of North American prehistory. But as paleontologists discovered closely related species in Asia—including Tarbosaurus bataar and Zhuchengtyrannus magnus—questions mounted about where this lineage truly began.In the new study, Morrison and his colleagues applied a model-based biogeographic approach to determine the most likely ancestral distribution of advanced tyrannosaurids. Their results placed the roots of the T. rex family tree in Late Cretaceous Asia, particularly during the Campanian and Maastrichtian ages, which spanned roughly 83 to 66 million years ago.
Into the Land of Giants
At the time of this migration, the Earth looked very different. The western portion of North America, known as Laramidia, was an isolated landmass separated from the east by the vast Western Interior Seaway. The Bering land bridge, now submerged beneath the Bering Strait, provided a temporary corridor for species to cross between Asia and North America as sea levels rose and fell.
The new findings imply that the ancestors of T. rex undertook this journey, entering Laramidia and ultimately outcompeting or replacing native tyrannosaurids such as Daspletosaurus. The study suggests this migration may have played a role in the extinction or ecological displacement of those earlier predators.
Parallel Lives, Half a World Apart
Though separated by thousands of miles, T. rex and its close Asian relative Tarbosaurus evolved in remarkably similar ways. Both reached lengths of 10 to 12 meters, possessed two-fingered forelimbs, and developed bone-crushing bite forces among the strongest of any terrestrial animal. Their shared evolutionary trajectory, despite geographic distance, mirrors convergent patterns seen in modern species like wolves and Tasmanian thylacines.
Like T. rex, Tarbosaurus was a top predator that likely hunted hadrosaurid dinosaurs and scavenged carcasses in Late Cretaceous floodplain environments. Histological studies have shown that both species experienced a rapid adolescent growth spurt, reaching full size in about two decades.
There are differences, too. Tarbosaurus had a narrower skull and may have relied less on binocular vision than its North American cousin. Its prey likely included sauropods and therizinosaurs, which were more common in its environment. Still, the two predators played comparable ecological roles on their respective continents.
Rewriting the Paleontological Narrative
The implications of the new research are wide-ranging, both for scientists who study dinosaur evolution and for the public who have long associated T. rex with the North American West. It reframes T. rex not as an endemic giant of the continent but as a descendant of ancient migrants whose lineage spans hemispheres.
The new study builds on more than a decade of prior research. In 2016, paleontologists Stephen Brusatte and Thomas Carr published a landmark phylogenetic analysis that showed T. rex was more closely related to Asian tyrannosaurids than to earlier North American species like Daspletosaurus. Earlier, a 2013 paper by Mark Loewen and colleagues argued that sea level fluctuations influenced the isolation and dispersal of tyrannosaurids between Asia and North America.
Other discoveries have deepened the Asian connection. In 2006, Xu Xing and colleagues described Guanlong wucaii, a small, crested tyrannosauroid from the Late Jurassic of China. The animal exhibited both primitive and derived features, providing clues to the group’s early evolutionary history.
The accumulating evidence now places T. rex within a broader migratory and evolutionary story, shaped by shifting continents, changing climates, and evolutionary pressures that played out over tens of millions of years.
Reassessing a Legend
Still, the study offers a striking revision of the predator’s past. T. rex, long seen as the sovereign of prehistoric North America, turns out to have roots in another hemisphere. Its ancestors may have arrived not as conquerors, but as opportunists in a world of shifting seas and ecological turnover.
The authors are careful not to overstate the case. They acknowledge that more fossil discoveries in Asia and North America will be needed to refine the timing and routes of tyrannosaurid dispersal. They also emphasize the importance of the North American fossil record in understanding T. rex‘s final evolutionary stage.
By placing T. rex within a broader evolutionary and geographic context, researchers are not just tracing its ancestry. They are revealing how ancient ecosystems connected across continents and demonstrating that even the fiercest animals of deep time were subject to the forces of migration, climate, and extinction. This recognition parallels the story of human evolution, in which ancestors moved across lands and changed with their environments.
Ancient Migrations, Modern Insights
This discovery comes at a time when scientists are using increasingly sophisticated tools to revisit longstanding assumptions about the deep past. As with the study of human origins, where ancient migrations and intercontinental movements have rewritten textbooks, dinosaur paleontology is now revealing similar patterns among extinct species.
“This migration would have brought a new apex predator into Late Cretaceous ecosystems in North America, potentially changing the dynamics of prehistoric food webs,” according to the Natural History Museum in London, which reported on the study’s publication in May 2025. By uncovering a deeper lineage for T. rex, researchers offer more than a taxonomic update. They highlight the fluidity of prehistoric life and show how the world’s most iconic dinosaur was part of a vast and dynamic web of evolutionary change.
Bibliography:
Brusatte, Stephen L., and Thomas D. Carr. “The Phylogeny and Evolutionary History of Tyrannosauroid Dinosaurs.” Scientific Reports, vol. 6, 2016, p. 20252. https://doi.org/10.1038/srep20252.
Loewen, Mark A., et al. “Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans.” PLOS ONE, vol. 8, no. 11, 2013, e79420. https://doi.org/10.1371/journal.pone.0079420.
Morrison, Cassius, et al. “Tyrannosaurus rex’s Ancestors Were Predatory Asian Dinosaurs.” Royal Society Open Science, vol. 12, no. 5, 2025, p. 242238. https://doi.org/10.1098/rsos.242238.
Xu, Xing, et al. “A Basal Tyrannosauroid Dinosaur from the Late Jurassic of China.” Nature, vol. 439, no. 7077, 2006, pp. 715–718. https://doi.org/10.1038/nature04511.
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