Paleontologists are divided on the origin of certainly one of our favourite dinosaurs, Tyrannosaurus rex. Some say its ancestry is firmly rooted in North America. Others aren’t satisfied.
A global staff, led by paleoecologist Cassius Morrison from College School London, now proposes the horrible lizard’s ‘grandparents’ might have as an alternative migrated to North America from Asia throughout the Bering Strait.
“Dozens of T. rex fossils have been unearthed in North America however our findings point out that the fossils of T. rex‘s direct ancestor might lie undiscovered nonetheless in Asia,” Morrison says.
“That is according to previous analysis discovering that the T. rex was extra carefully associated to Asian cousins such because the Tarbosaurus than to North American family reminiscent of Daspletosaurus.”
In 2024 a scientific staff reported {that a} fossil present in New Mexico, from the T. rex relative Tyrannosaurus mcraeensis, predated its extra well-known counterpart by round 6 million years. They took this to imply that large-bodied tyrannosaurs had a North American origin.
Morrison’s staff argues this conclusion – and the age estimated for T. mcraeensis – is unreliable, because of the shortage of specimens and present technological limitations.
Their strategies for tracing Tyrannosaur household historical past as an alternative concerned modeling based mostly on the fossil document (and its gaps), the dinosaur evolutionary tree and knowledge on the local weather and geography of the time. It notably reveals how tyrannosaurids and megaraptors might have moved throughout the continents.
Primarily based on these fashions, the staff argues that though the T. rex genus possible arose in western North America – or slightly the prehistoric continent Laramidia, because the land mass of the time is understood – its direct ancestors possible migrated throughout from Asia.
“The genus Tyrannosaurus originated in Laramidia from an ancestrally Asian taxon that emigrated to North America in the course of the Late Campanian – Early Maastrichtian,” the authors write.
This is not a brand new proposition: even the tiniest of T. rex‘s family left fossils that recommend a Beringian land bridge migration.
Megaraptors, they discovered, in all probability emerged in Asia round 120 million years in the past, earlier than dispersing to Europe and the southern ‘supercontinent’ Gondwana. However no megaraptor fossils have been present in Europe or Africa – a minimum of, not but.
“Initially of their evolutionary historical past, round 120 million years in the past, megaraptors had been a part of a widespread and various dinosaur fauna,” explains paleontologist Mauro Aranciaga Rolando, from the Bernardino Rivadavia Pure Sciences Argentine Museum.
“Because the Cretaceous interval progressed and the continents that when fashioned Gondwana started to float aside, these predators grew to become more and more specialised. Whereas in areas like Asia megaraptors had been ultimately changed by tyrannosaurs, in areas reminiscent of Australia and Patagonia they developed to grow to be apex predators, dominating their ecosystems.”
Because the world’s local weather grew to become cooler round 92 million years in the past, each megaraptors and tyrannosaurids reached gigantic sizes. However the staff discovered no direct correlation between local weather and gigantism in these dinosaurs. As a substitute, they might have been higher tailored to the chilly, permitting them to take over the newly vacant apex predator area of interest of their environments.
“They possible grew to such gigantic sizes to exchange the equally large carcharodontosaurid theropods that went extinct about 90 million years in the past,” says UCL paleontologist Charlie Scherer. “This extinction possible eliminated the ecological barrier that prevented tyrannosaurs from rising to such sizes.”
The analysis is printed in Royal Society Open Science.
