For decades, scientists have disagreed about where the mighty Tyrannosaurus rex truly came from. Many fossils of T. rex have been uncovered across western North America, leading to the belief that the species evolved entirely on the continent. But a growing body of research has suggested that this famous predator may have deeper roots elsewhere.
Now, new modelling and comparative fossil analysis have added compelling evidence that the ancestors of T. rex likely migrated into North America from Asia long before the species rose to dominance.
This article is for general informational purposes only and is based on current research, which may continue to evolve as new discoveries are made.
A Fresh Look At An Old Debate
The research, led by paleoecologist Cassius Morrison from University College London, re-examined previous fossil evidence and compared it with climate, geography, and migration models from the Late Cretaceous period. While T. rex itself is known entirely from western North America, Morrison’s team suggests that its direct ancestors likely originated in Asia before crossing into North America over the ancient Bering land connection.
This finding aligns with earlier work showing that T. rex shares closer anatomical and evolutionary ties with Asian tyrannosaurs like Tarbosaurus, rather than some of the earlier large tyrannosaurs found in North America.
Fossils That Complicate The Story
In 2024, another research group described a fossil from New Mexico belonging to Tyrannosaurus mcraeensis, a relative that may predate T. rex by about six million years. That discovery was used to support a North American origin. However, Morrison’s team cautions that the fossil record is still extremely limited and the age of the New Mexico remains is not yet firmly established.
Rather than relying on a single fossil or isolated specimen, the new study analyzed patterns across the entire tyrannosaur family tree, taking into account gaps in the fossil record as well as shifts in land and climate over millions of years.
How Tyrannosaurs May Have Moved Across Continents
The Late Cretaceous world looked very different from today. North America was split into two landmasses, and a land corridor periodically connected Asia to what is now Alaska. The team’s modelling suggests that smaller ancestral tyrannosaurs could have crossed into the continent during a time when the land bridge was exposed, eventually giving rise to the iconic T. rex on the western landmass known as Laramidia.
This migration model also helps explain why so many early and mid-sized tyrannosaurs are found in Asia, while only the very largest forms dominated North America toward the end of the Cretaceous.
The Role Of Climate And Competition
The study also explored why tyrannosaurs eventually grew so large. Around 92 million years ago, global climates cooled, and various large predator lineages declined. The extinction of giant carcharodontosaurid predators may have opened ecological space for tyrannosaurs to grow larger and assume top predator roles.
As paleontologist Charlie Scherer from UCL explains, the giants we know today likely rose not only because of climate shifts but also because their competition disappeared, creating an opportunity for tyrannosaurs to expand in size and territory.
What This Means For Future Discoveries
If the T. rex lineage truly began in Asia, as the models suggest, paleontologists now have reason to search for missing ancestral species in regions where fossils have not yet been fully explored. Morrison notes that the fossils of T. rex’s direct ancestors may still be buried in Asian rock formations waiting to be found.
As with many dinosaur mysteries, the story is still unfolding. Each fossil discovery has the potential to shift the timeline or reveal new evolutionary connections. But for now, this research strengthens a narrative that has been gaining momentum: the king of the dinosaurs may have crossed continents before taking its throne.
