Unveiling the King: New Insights into the Enigmatic Origins of Tyrannosaurus Rex

The genus Tyrannosaurus had its direct ancestors migrate from Asia over 70 million years ago, according to a groundbreaking study conducted by researchers at University College of Paleontologists in London.

This research, led by Cassius Morrison, a Ph.D. student at University College London, indicates that the rapid increase in the size of tyrannosaur dinosaurs and their close relatives, the Megaraptors, coincided with a global climate cooling that followed a temperature peak 92 million years ago.

This finding suggests that Tyrannosaurus Rex and its relatives may have been better adapted to cooler climates compared to other dinosaur groups at the time, likely due to their feathers and warmer physiology.

The geographical origins of Tyrannosaurus Rex have been a topic of intense debate,” stated Morrison.

“Paleontologists remain divided over whether their ancestors originated from Asia or North America.”

“Our modeling indicates that the “grandparents” of Tyrannosaurus Rex likely migrated to North America from Asia, crossing the Bering Strait between modern-day Siberia and Alaska.”

“This aligns with prior research showing that Tyrannosaurus Rex shares a closer relation to Asian relatives like Turbosaurus than to North American relatives such as Daspletosaurus.

“Numerous Tyrannosaurus Rex fossils have been found in North America, but our findings imply that the direct ancestors of this group may not yet have been unearthed in Asia.”

Paleontologists concluded that Tyrannosaurus Rex actually evolved in North America, particularly in Lalamidia, and was widely distributed across the region.

This conclusion contradicts last year’s findings suggesting that Tyrannosaurus mcraeensis, discovered in New Mexico, could be North American ancestors of Tyrannosaurus Rex from 3 to 5 million years ago. The team argued that the fossils of Tyrannosaurus mcraeensis were not properly dated.

For this study, researchers examined the migratory patterns of Tyrannosaurus and its relatives across the globe.

They employed mathematical models that represented fossils, dinosaur evolutionary trees, as well as the geography and climate of the era.

Importantly, the model addressed gaps in the fossil record and factored in uncertainties in the calculations.

Megaraptors are considered one of the most enigmatic large carnivorous dinosaurs.

In contrast to Tyrannosaurus Rex, they evolved slender heads and limbs as long as human height, with claws measuring up to 35 cm (14 inches).

Scientists conclude that Megaraptors were more widely distributed than previously thought, first appearing in Asia around 120 million years ago, spreading to Europe, and likely reaching Gondwana (encompassing regions of present-day Africa, South America, and the Southwest).

This suggests that Megaraptors inhabited regions like Europe and Africa, where no fossils had been found before.

They may have adapted differently from their Tyrannosaurus relatives, perhaps utilizing their claws for hunting instead of relying on powerful bites.

In South Gondwana, they could have preyed on small sauropods, while Tyrannosaurus Rex hunted large herbivores such as Triceratops, Edmontosaurus, and Ankylosaurus.

Both Tyrannosaurids and Megaraptors grew to enormous sizes nearly simultaneously as the climate cooled after the Cretaceous thermal peak 92 million years ago.

This rapid growth occurred following the extinction of other giant carnivorous dinosaurs, Carcharodontosaurids, which left a void at the top of the food chain.

The authors suggest that both Tyrannosaurus and Megaraptor could utilize cooler temperatures more effectively than their rival dinosaur groups.

By the end of the dinosaur age, Tyrannosaurus Rex weighed up to 9 tons (similar to very large African elephants and light tanks), while the Megaraptor reached lengths of up to 10 meters.

“Our findings illuminate the emergence of the largest tyrannosaurs in North and South America during the Cretaceous period and how they thrived by the end of the dinosaur epoch,” remarked Charlie Scheller of the University of London.

“They may have achieved their massive size to fill the ecological role left by the similarly large Carcharodontosaurid theropods that went extinct approximately 90 million years ago.”

“This extinction likely removed any ecological barriers that previously constrained the growth of tyrannosaurs.”

“Around 120 million years ago, Megaraptors were part of a diverse array of dinosaur species,” stated Dr. Mauro Alanciagaroland, a paleontologist at the Museum of Natural Sciences and the Bernardino Rivadavia Museum in Argentina.

“As the Cretaceous period progressed and the continents began to drift apart, these predators became increasingly specialized.”

“Such evolutionary shifts prompted them to adapt to more specific habitats.

“In areas like Asia, Megaraptors were ultimately replaced by Tyrannosaurus, but in regions like Australia and Patagonia, they became apex predators, dominating these ecosystems.”

This study is published in the journal Royal Society Open Science.

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Cassius Morrison et al. 2025. The Rise of the King: the origins of Gondwanan and the evolution of the Megaraptor dinosaurs. R. Soc. Open Sci. 12(5): 242238; doi: 10.1098/rsos.242238