Scientists from the University of Calgary have identified a new species of tyrannosaur that they describe as the "missing link" in the evolution of the world's most famous predatory dinosaurs, according to research published Wednesday in the journal Nature.
The newly named species, Khankhuuluu mongoliensis — meaning "Dragon Prince of Mongolia" — lived approximately 86 million years ago and represents a crucial evolutionary step between smaller tyrannosauroids and apex predators like Tyrannosaurus rex.
The fossils that revealed this new species had been hiding in plain sight for half a century. Originally excavated from Mongolia's Gobi Desert in the early 1970s, the partial skeletons of two individuals were misidentified as belonging to another tyrannosaur species, Alectrosaurus12.
The bones sat largely untouched in drawers at the Institute of Paleontology of the Mongolian Academy of Sciences until PhD student Jared Voris examined them during a 2023 research trip to Mongolia34.
"He was there a couple of years ago on this research trip and looked at the fossil and texted me [that] he thought it was a new species," study co-author Darla Zelenitsky, an associate professor at the University of Calgary, told The Canadian Press4.
Khankhuuluu measured about 13 feet in length and weighed approximately 1,700 pounds — roughly the size of a large horse12. This places it between the smaller, earlier tyrannosauroids that weighed only a few hundred pounds and the massive tyrannosaurs that could reach up to 5,000 pounds34.
The species possessed characteristics that distinguish it from both its ancestors and descendants. Unlike the bone-crushing T. rex, Khankhuuluu had a long, shallow skull that prevented it from crunching through bone, making it what researchers call a "mesopredator" — similar to modern coyotes that rely on speed and agility56.
"This missing link was around 750 kilograms. Its ancestors were a couple of hundred kilograms and just tiny, but then when you get to tyrannosaurs proper, they were over a thousand kilograms," Zelenitsky told The Canadian Press4.
The discovery suggests that Khankhuuluu or a closely related species migrated from Asia to North America via a land bridge connecting Siberia and Alaska roughly 85 million years ago12. This migration preceded the rise of North American tyrannosaurs by about 20 million years.
"This discovery forced us to look at the family tree of tyrannosaurs in a very different light. It ended up with us rewriting the family history of tyrannosaurs," Zelenitsky said3.
