The grandfather of Tyrannosaurus rex arrived through the Bering Strait to North America

▲ A study found that the rapid growth in size of tyrannosaurids coincided with a cooling of the global climate 92 million years ago. Photo taken from the University of London website / Pedro Salas and Sergey Krasovskiy

Europa Press

La Jornada Newspaper, Friday, May 9, 2025, p. 6

Madrid. Tyrannosaurus rex evolved in North America, but its direct ancestor came from Asia, crossing a land bridge that connected the continents more than 70 million years ago.

A new study led by researchers at UCL (University College London), published in the journal Royal Society Open Science , also reveals that the rapid growth of tyrannosaurids (the group that included rex ), as well as a closely related group called megaraptors, coincided with a cooling of the global climate following a peak in temperatures 92 million years ago.

This suggests that the rex and its cousins ​​may have been better adapted to colder climates than other dinosaur groups of the time, perhaps due to their plumage or a more warm-blooded physiology.

The international team included researchers from the universities of Oxford, Pittsburgh, Aberdeen (Arizona), Anglia Ruskin (Oklahoma) and Wyoming.

Lead author Cassius Morrison, a PhD student in Earth sciences at UCL, said in a statement: “The geographical origin of Tyrannosaurus rex is the subject of intense debate. Paleontologists have been divided over whether its ancestor came from Asia or North America. Our model suggests that its grandparents likely arrived in North America from Asia, crossing the Bering Strait between what is now Siberia and Alaska.”

This is consistent with previous research indicating that the rex was more closely related to Asian cousins ​​like Tarbosaurus than to North American relatives like Daspletosaurus .

“Dozens of Tyrannosaurus rex fossils have been unearthed in North America, but our findings indicate that fossils of its direct ancestor may still remain undiscovered in Asia,” he added. The research team concluded that the rex itself evolved in North America, specifically in Laramidia, the western half of the continent, where it was widely distributed.

He had no local ancestry

These researchers disagree with findings published last year that a rex relative, Tyrannosaurus mcraeensis , found in New Mexico, predated the rex by 3 to 5 million years, a finding that pointed to its North American ancestry. The team argued that this mcraeensis fossil was not reliably dated.

For the new study, researchers explored how tyrannosaurids and their cousins, the megaraptors, moved around the world. They used mathematical models based on fossils, dinosaur evolutionary trees, and the geography and climate of the time. Importantly, the models account for gaps in the fossil record, incorporating uncertainty into the calculations.

Megaraptors are considered the most mysterious of the large carnivorous dinosaurs, as few fossils have been found. Unlike the rex , they evolved slender heads and arms as long as a person, with claws up to 35 centimeters long.

The researchers concluded that megaraptors were more widely distributed around the world than previously thought, probably originating in Asia about 120 million years ago and spreading to Europe and then the great southern landmass of Gondwana (including present-day Africa, South America and Antarctica).

This would mean that megaraptors lived in parts of the world (Europe and Africa) where no fossils of them have been found to date.

They may have evolved differently from their tyrannosaurid cousins, with lethal claws instead of a powerful bite, because they hunted different prey. In southern Gondwana, they may have fed on sauropods (juveniles), while Tyrannosaurus rex hunted Laramidian species such as Triceratops, Edmontosaurus, and Ankylosaurus.

Gigantic sizes

Both tyrannosaurids and megaraptors reached gigantic sizes at virtually the same time, as the climate cooled following a spike in global temperatures known as the Cretaceous Thermal Maximum 92 million years ago. This rapid growth occurred after the extinction of other giant carnivores, the carcharodontosaurids, leaving a gap at the top of the food chain.

Experts suggested that tyrannosaurs, both tyrannosaurids and megaraptors, may have been able to take better advantage of the cooler temperatures than rival dinosaur groups.

At the end of the age of dinosaurs, Tyrannosaurus rex weighed up to nine tons (about the same as a very large African elephant or a light tank), while megaraptors reached lengths of 10 meters.