PARIS - Misidentified bones that languished in the drawers of a Mongolian institute for 50 years belong to a new species of tyrannosaur that rewrites the family history of the mighty T-Rex, scientists said on Wednesday.
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This slender ancestor of the massive Tyrannosaurus Rex was around four metres long and weighed three quarters of a tonne, according to a new study in the journal Nature.
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“It would have been the size of a very large horse,” study co-author Darla Zelenitsky of the University of Calgary in Canada told AFP.
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The fossils were first dug up in southeastern Mongolia in the early 1970s but at the time were identified as belonging to a different tyrannosaur, Alectrosaurus.
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For half a century, the fossils sat in the drawers at the Institute of Paleontology of the Mongolian Academy of Sciences in the capital Ulaanbaatar.
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Then PhD student Jared Voris, who was on a trip to Mongolia, started looking through the drawers and noticed something was wrong, Zelenitsky said.
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It turned out the fossils were well-preserved, partial skeletons of two different individuals of a completely new species.
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“It is quite possible that discoveries like this are sitting in other museums that just have not been recognised,” Zelenitsky added.
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They named the new species Khankhuuluu mongoliensis, which roughly means the “dragon prince” of Mongolia because it is smaller than the “king” T-Rex.
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Zelenitsky said the discovery “helped us clarify a lot about the family history of the tyrannosaur group because it was really messy previously”.
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The T-Rex represented the end of the family line.
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It was the apex predator in North America until 66 million years ago, when an asteroid bigger than Mount Everest slammed into the Gulf of Mexico.
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Three quarters of life on Earth was wiped out, including all the dinosaurs that did not evolve into birds.
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Around 20 million years earlier, Khankhuuluu — or another closely related family member — is now believed to have migrated from Asia to North America using the land bridge that once connected Siberia and Alaska.
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This led to tyrannosaurs evolving across North America.
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Then one of these species is thought to have crossed back over to Asia, where two tyrannosaur subgroups emerged.
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One was much smaller, weighing under a tonne, and was nicknamed Pinocchio rex for its long snout.
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The other subgroup was huge and included behemoths like the Tarbosaurus, which was only a little smaller than the T-rex.
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One of the gigantic dinosaurs then left Asia again for North America, eventually giving rise to the T-Rex, which dominated for just two million years — until the asteroid struck.