A groundbreaking study led by researchers from UCL has uncovered new insights into the origins of Tyrannosaurus rex, suggesting that this iconic predator likely migrated from Asia to North America via a land bridge more than 70 million years ago. Published in the Royal Society Open Science, the research not only highlights T. rex's migration patterns but also delves into the evolutionary rise of megaraptors, indicating that climate played a pivotal role in their development.
About 92 million years ago, global temperatures peaked, followed by a significant cooling trend. This climatic shift coincided with a rapid increase in the size of both tyrannosaurids and megaraptors. Interestingly, Morrison's team found no direct correlation between temperature and body mass. Instead, they propose that these climatic changes may have indirectly fueled the phenomenon of gigantism by altering predator-prey dynamics. “Our modelling suggests the ‘grandparents’ of T. rex likely came to North America from Asia, crossing the Bering Strait between what is now Siberia and Alaska,” stated lead author Cassius Morrison, a PhD student in Earth Sciences at UCL.
The origins of T. rex have been a contentious topic among paleontologists. While some researchers maintain that T. rex originated in North America, Morrison's findings lend credence to the idea that its direct ancestor migrated from Asia. This theory aligns with previous studies that have linked T. rex to Asian relatives, such as Tarbosaurus. Despite the abundance of T. rex fossils found in North America, Morrison speculates that the fossils of its direct ancestor may still be waiting to be discovered in Asia.
In 2022, a study suggested that the fossil Tyrannosaurus mcraeensis, found in New Mexico, predated T. rex by three to five million years. However, Morrison's team disputes this claim, arguing that the fossil's dating is unreliable. Instead, their biogeographical model positions T. rex as a North American species that evolved in Laramidia, a region that once stretched from Alaska to Mexico.
While T. rex ruled the northern continents, megaraptors thrived in Gondwana, an ancient supercontinent that encompassed South America, Africa, Antarctica, Australia, and India. These predators, characterized by slender heads, long arms, and 35-centimeter claws, took a distinct evolutionary route. Morrison's team traced the origins of megaraptors to Asia around 120 million years ago, from where they spread to Europe, Africa, and throughout Gondwana. Despite their widespread presence, fossils of megaraptors remain scarce, leading to significant gaps in the evolutionary timeline.
Unlike the formidable bone-crushing jaws of T. rex, megaraptors employed their massive claws to hunt. In the southern regions of Gondwana, these predators likely preyed on juvenile sauropods, while T. rex targeted larger herbivores like Triceratops and Edmontosaurus in Laramidia. Both groups reached gigantic sizes, particularly as temperatures declined and the carcharodontosaurids—another group of large predators—faced extinction. Morrison's team theorizes that the disappearance of these giants opened the apex predator niche, allowing both tyrannosaurids and megaraptors to grow in size.
While the study establishes a link between cooler climates and larger dinosaur sizes, it emphasizes that there is no direct correlation between temperature and body mass. Instead, Morrison's team suggests that climatic shifts may have indirectly propelled gigantism by reshaping ecosystems and influencing prey availability. By the end of the Cretaceous period, T. rex could weigh up to nine tonnes, comparable to a large African elephant, whereas megaraptors could reach lengths of over 10 meters.
Dr. Mauro Aranciaga Rolando from the Natural Sciences Argentine Museum emphasizes the significance of Gondwana in shaping the evolution of megaraptors. As the continents drifted apart, megaraptors adapted to diverse environments, becoming apex predators in regions like Australia and Patagonia. “While in areas like Asia, megaraptors were eventually supplanted by tyrannosaurs, in regions such as Australia and Patagonia, they evolved to dominate their ecosystems,” Rolando noted.
In conclusion, Morrison's study underscores the necessity for more fossil evidence to refine the evolutionary timeline of megaraptors. As regions like Africa and Antarctica remain largely unexplored, they may harbor critical clues to understanding megaraptor dispersal and the factors contributing to their gigantism. For now, the study firmly positions T. rex as a North American genus with Asian roots that are still shrouded in mystery, while the evolutionary story of megaraptors remains intriguingly incomplete. This comprehensive research is published in the Royal Society Open Science.
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