How T. Rex’s Ancestors Journeyed from Asia to North America: The Incredible Migration Story

A new study from UCL has revealed that the famous Tyrannosaurus rex likely originated in Asia. Researchers discovered that ancestors of T. rex crossed a land bridge from Asia to North America over 70 million years ago. This finding may shift how we view the evolution of this colossal predator.

Published in Royal Society Open Science, the study not only explores T. rex’s migration path but also investigates the evolutionary development of megaraptors. This evolution seems to be linked to climate change during that period.

About 92 million years ago, the Earth experienced warmer temperatures, but this was followed by a cooling trend. Interestingly, this climatic shift coincided with the growth spurt of several dinosaur species, including tyrannosaurids and megaraptors. However, the study’s authors, including PhD student Cassius Morrison, noted there’s no straightforward link between temperature and size. Instead, they propose that changing climates affected predator-prey dynamics, indirectly influencing the size of these dinosaurs.

Morrison explains, “Our modeling indicates that the ancestors of T. rex likely migrated to North America via the Bering Strait, connecting Siberia with Alaska.” This supports theories that link T. rex with its Asian relatives like Tarbosaurus.

Debates about T. rex’s origins continue among scientists. While many fossils have been found in North America, Morrison believes their direct ancestors’ fossils in Asia remain yet to be discovered. Last year, a study introduced Tyrannosaurus mcraeensis, a potential predecessor from New Mexico, but Morrison’s team contests its dating as unreliable. Instead, they assert that T. rex evolved in North America, particularly in an area known as Laramidia.

Meanwhile, megaraptors thrived in southern landmasses. These predators evolved in Asia around 120 million years ago, later spreading to places like Africa and South America. Despite their wide distribution, megaraptor fossils are scarce, creating gaps in our understanding of their evolution.

Unlike T. rex, which had powerful jaws, megaraptors hunted differently. With long arms and massive claws, they likely targeted smaller prey like juvenile sauropods, while T. rex took down larger dinosaurs such as Triceratops.

By the end of the Cretaceous period, T. rex reached sizes comparable to large African elephants, weighing up to nine tons. This growth, according to co-author Charlie Scherer, is connected to the extinction of giant predators called carcharodontosaurids. “These changes in the ecosystem created opportunities for tyrannosaurids and megaraptors to grow larger,” he says.

Dr. Mauro Aranciaga Rolando from the Natural Sciences Argentine Museum emphasizes the influence of ancient continents on megaraptor evolution. As continents shifted, megaraptors adapted to diverse habitats, becoming apex predators in locations like Australia. “While megaraptors disappeared from Asia due to competition with tyrannosaurs, they thrived in places like Patagonia,” he explains.

Morrison’s study shows that we still need more fossil evidence to piece together the timeline of megaraptor evolution. Underexplored regions like Africa and Antarctica could offer vital clues. For now, it seems T. rex found its place in North America, sharing a mysterious lineage with Asia, while megaraptors’ stories are still unfolding.

The study is available in the journal Royal Society Open Science.

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