Evrim Yazgin
Cosmos science journalist
Fossils found in Mongolia of a new dinosaur species may help palaeontologists explain the evolution and dispersal of the group which includes Tyrannosaurus rex.
T. rex is often called the “king of the dinosaurs” for good reason. It was the apex predator for 2 million years before it and all the non-avian dinosaurs went extinct 66 million years ago. T. rex was massive – measuring 4m tall, 12m long and 9 tonnes.
How it evolved to dominate ancient North America is debated.
T. rex was the biggest, but it wasn’t the only large-bodied carnivore in its immediate family – a group called Eutyrannosaurians. In Asia, the tyrannosaurid Tarbosaurus grew to almost the same size as T. rex. In the polar north, there was the 9m-long Albertosaurus. And before T. rex dominated North America, there was T. mcraeensis and Daspletosaurus.
Recent studies suggests that the ancestors of T. rex had smaller bodies and originated in Asia, before travelling east to the Americas across ancient land bridges. But there has been little direct fossil evidence of this evolution.
Now a paper published in Nature describes a new species found in Mongolia which adds evidence to this Asian origin story of T. rex and its kin.
Khankhuuluu mongoliensis lived about 85 million years ago (mya). It is known from 2 partial skeletons which were originally discovered in Mongolia in 1972–73, but have been reanalysed to assign the new species.
The species sits just outside the Eutyrannosaurian group and is an immediate ancestor to 2 clades within this group: the massive, deep-snouted Tyrannosaurini and smaller, shallow-snouted Alioramini dinosaurs.
K. mongoliensis would have had a skull about 70cm long – less than half the size of an adult T. rex’s.
“Our study reveals that Eutyrannosauria originated in North America as a result of a dispersal event of mid-grade tyrannosauroids from Asia like Khankhuuluu,” the authors write. “Eutyrannosauria then radiated in North America over a relatively short period of time (more than 15 species in 15 million years).”
