Paleontologists have long debated the origins of one of the most iconic dinosaurs, the Tyrannosaurus rex. While many fossils have been found in North America, some researchers questioned whether the species truly originated there or if its ancestors migrated from elsewhere.
A recent study led by paleoecologist Cassius Morrison from University College London sheds new light on this mystery, suggesting that the direct ancestors of T. rex may have migrated from Asia across the ancient Bering Strait.
Tracing Tyrannosaurus rex Migration Across Continents
The international research team used models that combined the fossil record, dinosaur evolutionary trees, and climate and geographic data of the Late Cretaceous period. Morrison explains, “Dozens of T. rex fossils have been unearthed in North America, but our findings indicate that the fossils of T. rex‘s direct ancestor may lie undiscovered still in Asia,”
This aligns with previous studies showing that T. rex was more closely related to Asian relatives such as Tarbosaurus than to other North American tyrannosaurids like Daspletosaurus.
In 2024, another team reported a fossil of Tyrannosaurus mcraeensis found in New Mexico that predates T. rex by about six million years. This led some to argue that large tyrannosaurs originated in North America. However, Morrison’s group challenges this claim, citing the limited number of specimens and technological constraints affecting the age estimates.
The Untold Story Of Dinosaur Predators Taking Over
The team highlights that fossils of small tyrannosaur relatives have suggested migration via the Beringian land bridge, which connected Asia and North America. The study further details the evolutionary journey of other predatory dinosaurs like megaraptors, which originated in Asia around 120 million years ago.
These predators later spread to Europe and Gondwana, the southern supercontinent. Paleontologist Mauro Aranciaga Rolando from Argentina’s Bernardino Rivadavia Natural Sciences Museum points out that megaraptors were “part of a widespread and diverse dinosaur fauna” early in their evolution.
Over time, as continents drifted apart, megaraptors became highly specialized. In regions such as Asia, tyrannosaurs eventually replaced them, while in Australia and Patagonia, megaraptors evolved into apex predators dominating their ecosystems.
Gigantism And Environmental Adaptation In Tyrannosaurs And Megaraptors
The research reveals that around 92 million years ago, both megaraptors and tyrannosaurids grew to enormous sizes as the global climate cooled. Yet, the study finds no direct link between climate change and this gigantism.
Instead, these dinosaurs may have adapted better to cooler environments, which allowed them to fill the apex predator niche left vacant after the extinction of giant carcharodontosaurid theropods around 90 million years ago.
Charlie Scherer, a paleontologist at UCL and co-author of the study, explains, “They likely grew to such gigantic sizes to replace the equally giant carcharodontosaurid theropods that went extinct about 90 million years ago. This extinction likely removed the ecological barrier that prevented tyrannosaurs from growing to such sizes.”
