University of Calgary paleontologists discover closest-known ancestor of T. rex

Paleontologists at the University of Calgary have just uncovered the closest-known ancestor to one of earth's most iconic predators: the mighty T-Rex.

The University of Calgary’s sports teams may be called the “Dinos,” but the school’s paleontologists just lived up to the name in a much bigger way — by unearthing the closest-known ancestor to the legendary Tyrannosaurs rex.

A new species of dinosaur named Khankhuuluu, meaning “dragon prince” in Mongolian, has been identified by a team of researchers led by UCalgary paleontologists Darla Zelenitsky and Jared Voris.

The discovery, published in the journal Nature, offers a rare glimpse into a key transitional stage in Tyrannosaur evolution — when they were still mid-sized, agile predators rather than bone-crushing giants.

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“This new species provides us the window into the ascent stage of Tyrannosaur evolution,” said Voris, a PhD candidate in the department of earth, energy and environment.

“Right when they’re transitioning from small predators to their apex predator form, this was a fast, nimble mesopredator — something like a prehistoric coyote.”

Khankhuuluu lived approximately 86-million years ago and weighed about 750 kilograms — the size of a modern horse, and a far cry from the massive Tyrannosaurus rex famously depicted in the Jurassic Park movie franchise.

Its fossils were originally found in the Bayanshiree Formation in southeastern Mongolia in the 1970s by paleontologist Altangerel Perle who likened the fossils to another medium-sized Tyrannosaur called Alectrosaurus from China.

Voris went to Mongolia in 2023 to study fossils at the Institute of Paleontology and soon realized there were features that differentiated them from the Alectrosaurus.

He found that unlike its iconic descendants, Khankhuuluu lacked the bone-crushing bite and massive build.

Instead, it featured a long, shallow skull and small rudimentary horns, likely used in mating displays or intimidation — features that later evolved into the more elaborate forms seen in Albertosaurus and Gorgosaurus.

“The first real identifier was that the nasal bone was had a big hollow cavity inside of it – and this is something we never see in Tyrannosaurs, it’s always been this really just massive bone so they can bite down really hard,” said Voris.

“That was the first clue that really told me that this was something else.”

Rewriting the Tyrannosaurs family tree

The discovery also has major implications for the geographic story of Tyrannosaurs.

According to Zelenitsky, Khankhuuluu – or a close relative – likely migrated from Asia to North America around 85 million years ago, where it gave rise to the line of apex predators that culminated in T. rex.

“Our study provides solid evidence that large Tyrannosaurs first evolved in North America as a result of this immigration event,” said Zelenitsky.

The fossil record also suggests that the movement of Tyrannosaurs between Asia and North America was more limited and directional than previously thought.

After evolving in North America, some Tyrannosaurs later returned to Asia, splitting into two evolutionary paths — one leading to massive predators like T. rex, and another to long-snouted, medium-sized species nicknamed “Pinocchio rexes.”

Zelenitsky says this discovery now provides a backstory to the evolutionary process of an entire dinosaur species.

“This is so important because it really told us what an ancestral Tyrannosaur looked like, and we ended up rewriting the family tree of Tyrannosaurs,” she said.

“But what’s missing is some of the earlier Tyrannosauroids, the animals that are older than Khankhuuluu, because that material tends to be less well preserved.

“There’s not as many specimens, so those need to be studied in more detail to figure out the far back ancestors of Tyrannosaurs.”

The UCalgary team now plans to dig even deeper into the past in search of the earlier ancestors that preceded Khankhuuluu.

In the meantime, the university’s namesake Dinos can now take pride in something no rival can match: their very own link to the king of the dinosaurs.