PARIS, June 11, 2025 (BSS/AFP) - 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 Wednesday. 

This slender ancestor of the massive Tyrannosaurus Rex was around four metres 
(13 feet) long and weighed three quarters of a tonne, according to a new 
study in the journal Nature.

"It would have been the size of a very large horse," study co-author Darla 
Zelenitsky of Canada's University of Calgary told AFP.

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.

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. 

Then PhD student Jared Voris, who was on a trip to Mongolia, started looking 
through the drawers and noticed something was wrong, Zelenitsky said.

It turned out the fossils were well-preserved, partial skeletons of two 
different individuals of a completely new species. 

"It is quite possible that discoveries like this are sitting in other museums 
that just have not been recognised," Zelenitsky added.

- 'Messy' family history -

They named the new species Khankhuuluu mongoliensis, which roughly means the 
dragon prince of Mongolia because it is smaller than the "king" T-Rex.

Zelenitsky said the discovery "helped us clarify a lot about the family 
history of the tyrannosaur group because it was really messy previously".

The T-Rex represented the end of the family line. 

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. 

Three quarters of life on Earth was wiped out, including all the dinosaurs 
that did not evolve into birds.

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.

This led to tyrannosaurs evolving across North America.

Then one of these species is thought to have crossed back over to Asia, where 
two tyrannosaur subgroups emerged. 

One was much smaller, weighing under a tonne, and was nicknamed Pinocchio rex 
for its long snout.

The other subgroup was huge and included behemoths like the Tarbosaurus, 
which was only a little smaller than the T-rex. 

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.