Before T. rex, there was the “dragon prince”

Voris, a PhD candidate in the Department of Earth, Energy, and Environment, explains that this newly identified Tyrannosaur lived about 86 million years ago. It was a medium-sized, fast-moving predator that evolved after the extinction of other large carnivorous dinosaurs.

A Glimpse Into Tyrannosaur Evolution

According to Voris, "This new species provides us the window into the ascent stage of Tyrannosaur evolution; right when they're transitioning from small predators to their apex predator form." Khankhuuluu is regarded as the nearest known ancestor of the colossal Tyrannosaurs popularized by films like Jurassic Park.

The name Khankhuuluu comes from Mongolian and translates to "prince of dragons" or "the dragon prince." The name reflects its position in the Tyrannosaur family tree -- standing as the "prince" before the "king," Tyrannosaurus rex. At roughly 750 kilograms (about the size of a horse), it was two to three times smaller than its enormous descendants but shared many of their defining traits.

Physical Traits and Hunting Style

Khankhuuluu displayed small horn-like structures on its head, features that later became more pronounced in later Tyrannosaur species such as Albertosaurus and Gorgosaurus, likely used for mating displays or intimidation. Its long, shallow skull indicates it lacked the bone-crushing bite strength of T. rex. Instead, scientists describe Khankhuuluu as a mesopredator, similar to modern coyotes, relying on speed and agility to hunt.

Fossils From Mongolia Tell a New Story

The fossils were unearthed from the Bayanshiree Formation in southeastern Mongolia and were first studied in the 1970s by paleontologist Altangerel Perle, who initially compared them to a similar species known as Alectrosaurus from China. When Voris examined the fossils in 2023 at the Institute of Paleontology in Mongolia, he noticed subtle but key differences that distinguished them from Alectrosaurus.

The Journey of Tyrannosaurs Between Continents

Dr. Zelenitsky explains that Khankhuuluu or a closely related species likely migrated from Asia to North America around 85 million years ago."Our study provides solid evidence that large Tyrannosaurs first evolved in North America as a result of this immigration event," she says.

The research suggests these migrations between Asia and North America were rarer and more limited than previously believed. Khankhuuluu appears to be the last known Asian ancestor of the Tyrannosaurs before their diversification in North America.

From the "Dragon Prince" to the Tyrant King

Scientists believe that Khankhuuluu, or one of its relatives, crossed a land bridge into North America, where it evolved into the formidable apex predator Tyrannosaurs. Fossil evidence shows that Tyrannosaurs thrived in North America for several million years before returning to Asia, where their lineage split into two branches: one evolved into massive predators like T. rex, while the other produced more slender, long-snouted types nicknamed "Pinocchio rexes."

What Comes Next in the Research

Looking ahead, the team plans to study earlier and less-understood ancestors of these apex predators to fill in the remaining gaps of the Tyrannosaur evolutionary story.