Palaeontologists have identified a new species of dinosaur, named Khankhuuluu, which is the closest-known ancestor to the gigantic tyrannosaurs.

The finding by an international team of researchers — led by Jared Voris and Dr. Darla Zelenitsky, PhD, in the Faculty of Science at the University of Calgary — has been published in the journal Nature.

“We identified a new species of tyrannosauroid, an ancestor to apex predatory tyrannosaurs,” says Jared Voris, first author on the paper and a PhD candidate in the Department of Earth, Energy and Environment. “Basically, right before they got to be these apex predators, tyrannosaurs were these medium-sized, fleet-footed predators that lived in the shadows of other apex predators.”

Something happened to the other non-tyrannosaur apex predators that led to their extinction. It left an opening for Khankhuuluu to evolve, and later became the behemoths famously depicted in films such as Jurassic Park.

“We’ve never really had a good representation of that transition,” explains Voris. “This new species actually provides us that window into the ascent stage of tyrannosaurs; right when they’re transitioning to the apex predator form.”

Before the king comes the prince

The name Khankhuuluu translates from Mongolian to mean either “prince of dragons” or “the dragon prince.”

“We wanted something to epitomize how it’s not quite the king yet,” explains Voris. “Tyrannosaurs are often referred to as kings of the Cretaceous and Tyrannosaurus rex means the tyrant lizard king, so we wanted something that comes before a king, which is a prince.”

Being the link between the smaller and apex predator tyrannosaur species, Khankhuuluu both shares and lacks certain characteristics of later species like Albertosaurus and Gorgosaurus.

The new species weighed 750 kilograms, about the size of a horse, making it two to three times smaller than its massive descendants. It had tiny rudimentary horns that would evolve to be prominent on later species for mating display and intimidation. Khankhuuluu had a long, shallow skull that shows it couldn’t crunch through bone the way a T. Rex could.

Using speed to ambush and take down prey

In fact, Khankhuuluu is best defined as a mesopredator, meaning it used speed and ambush to hunt prey versus the later apex predators who used sheer bulk to take down heavier animals. Think of Khankhuuluu as the jackal or hyena to a T. Rex’s lion.

The fossils used to identify the new species were found in the Bayanshiree Formation in southeastern Mongolia. They had been studied in the 1970s by Mongolian palaeontologist Altangerel Perle, who had likened the fossils to another medium-sized tyrannosauroid named Alectrosaurus from China.

Nearly 50 years later, Voris traveled to Mongolia to look at the fossils himself.

“I realized there were features that made this different from other Alectrosaurus fossils, and they also provided a lot more information into the evolutionary history of tyrannosaurs,” says Voris.

Species reveals migration path from Asia to North America

The discovery of Khankhuuluu reveals the movement of tyrannosauroids from Asia to North America.

“Khankhuuluu, or a closely related species, would have immigrated to North America from Asia around 85 million years ago,” explains Zelenitsky. “Our study provides solid evidence that large tyrannosaurs first evolved in North America as a result of this immigration event of ancestor tyrannosauroids.”

The research reveals that the species travelled from Asia over a land bridge into North America where it began to evolve into the famous apex predator.

The fossil record indicates these apex predators stuck around in North America for a few million years before reappearing in the fossil record in Asia, where there is a split in the lineage into two groups. One group branched off to become even bigger apex predators, ultimately evolving into T. Rex, and the other group evolved into a medium-sized, long-snouted species dubbed Pinocchio rexes.

Zelenitsky says the research allowed them to re-analyze the family tree of tyrannosaurs.

“Finding a new species is always very exciting,” she says. “It tells us how tyrannosaurs as a group became so diverse and successful at the end of the Cretaceous.”

Using dinosaurs to figure out how the world works now

Looking ahead, the next step for researchers is to investigate even earlier ancestors of the apex predators. It would require the discovery of more Asian tyrannosauroid fossils, as this paper is the summation of the entire known tyrannosaur fossil record.

“This shows that these animals were moving back and forth between North America and Asia,” says Voris. “That hasn’t changed. We have tons of evidence of patterns like this happening with wolves, deer, and humans, so it shows a lot of the patterns that we see in the modern day are things that were going on back when the dinosaurs were around.”

For Voris, the work also is a way to get the public engaged and involved in the natural sciences.

“Dinosaurs are cool, right,” says Voris. “It shows people this is what science does. We use the same methods that climate scientists and medical professionals use to try and figure out how the world works and why things work the way they do.”