Scientists disagree about the beginnings of one of our beloved species.
dinosaurs
,
Tyrannosaurus rex
.
Some believe its heritage is deeply ingrained in North America, while others remain unconvinced.
A global research group, headed by paleoecologist Cassius Morrison from University College London, suggests that the ancestors of these formidable creatures might have traveled to North America from Asia via the Bering Strait.
“Dozens of
T. rex
Fossils have been discovered in North America; however, our research suggests that the remains of
T. rex
‘May still be hiding an undiscovered direct ancestor in Asia,’ Morrison said.
says.
“This aligns with previous studies which found that the
T. rex
was more closely linked to Asian relatives like the
Tarbosaurus
than to North American relatives such as
Daspletosaurus.
”
In 2024, a group of scientists
reported
that a fossil discovered in New Mexico, from the
T. rex
relative
Tyrannosaurus mcraeensis,
predated its more famous counterpart by around 6 million years. They took this to mean that large-bodied tyrannosaurs had a North American origin.
Morrison’s team argues this conclusion – and the age estimated for
T. mcraeensis –
is deemed untrustworthy because of the limited number of samples available and present technology constraints.
Their methods for tracing
Tyrannosaur
family history rather focused on modeling derived from the fossil record (along with its omissions)
dinosaur
the evolutionary tree along with information about the climatic and geographic conditions during that period. This notably shows the development and characteristics of tyrannosaurids and their evolution.
megaraptors
might have traveled between different continents.
Based on these models, the team argues that although the
T. rex
genus likely arose in western North America – or rather the prehistoric continent
Laramidia
, as the land mass of the time is known – its direct ancestors likely migrated across from Asia.
“T
he genus
Tyrannosaurus
originated in Laramidia from an ancestrally Asian taxon that emigrated to North America during the Late Campanian – Early Maastrichtian,” the authors
write
.
This isn’t a new proposition:
even the tiniest
of
T. rex
‘s relatives left fossils that suggest a Beringian land bridge migration.
Megaraptors, they found, probably emerged in Asia around 120 million years ago, before dispersing to Europe and the southern ‘supercontinent’ Gondwana. But no megaraptor fossils have been found in Europe or Africa – at least, not yet.
“At the beginning of their evolutionary history, around 120 million years ago, megaraptors were part of a widespread and diverse dinosaur fauna,”
explains
paleontologist Mauro Aranciaga Rolando, from the Bernardino Rivadavia Natural Sciences Argentine Museum.
“As the Cretaceous period progressed and the continents that once formed Gondwana began to drift apart, these predators became increasingly specialized.
While in regions like Asia megaraptors were eventually replaced by tyrannosaurs, in areas such as Australia and Patagonia they evolved to become apex predators, dominating their ecosystems.”
As the world’s climate became cooler around 92 million years ago, both megaraptors and tyrannosaurids reached gigantic sizes. But the team found no direct correlation between climate and gigantism in these dinosaurs. Instead, they may have been better adapted to the cold, allowing them to take over the newly vacant apex predator niche in their environments.
“They likely grew to such gigantic sizes to replace the equally giant carcharodontosaurid theropods that went extinct about 90 million years ago,”
says
UCL paleontologist Charlie Scherer. “This extinction likely removed the ecological barrier that prevented tyrannosaurs from growing to such sizes.”
The research is published in
Royal Society Open Science
.
