A newly discovered mid-sized dinosaur from Mongolia is shedding new light on the evolutionary origins of the fearsome Tyrannosaurus rex. The species, named Khankhuuluu mongoliensis — meaning “Dragon Prince” in Mongolian — has been identified as a crucial precursor to the tyrannosaur lineage, offering fresh insights into how one of Earth’s most iconic predators came to be.

According to Reuters, Khankhuuluu mongoliensis, which lived approximately 86 million years ago during the Cretaceous Period, predates T. rex by roughly 20 million years. Measuring about 13 feet (4 meters) in length and weighing around 1,600 pounds (750 kilograms), the bipedal predator was considerably smaller and more lightly built than the giant T. rex, which could reach lengths of over 40 feet (12.3 meters).

dinosaur

The newly identified dinosaur species Khankhuuluu mongoliensis is shown in the timeline of the dinosaur lineage called tyrannosaurs, which included Tyrannosaurus rex, in this illustration released on June 11, 2025. Jared Voris/Handout via REUTERS THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. NO RESALES. NO ARCHIVES

Unlike its massive descendant, Khankhuuluu appears to have been a swift and agile hunter, likely preying on smaller creatures such as bird-like dinosaurs, including oviraptorosaurs and ornithomimosaurs. Its lengthy snout housed sharp, steak knife-like teeth designed for slashing rather than crushing prey.

“In the name, we wanted to capture that Khankhuuluu was a small, early form that had not evolved into a king. It was still a prince,” said paleontologist Darla Zelenitsky of the University of Calgary, who co-authored the study published on Wednesday in the journal Nature.

The discovery is based on fossils from two individuals excavated in Mongolia during the 1970s. These remains, which include parts of the skull, limbs, tail, and back bones, have only now been fully analyzed, offering a more complete picture of tyrannosaur evolution than previously available specimens.

“What started as the discovery of a new species ended up with us rewriting the family history of tyrannosaurs,” said Jared Voris, a University of Calgary doctoral student and the study’s lead author. Prior to this finding, the relationships between various tyrannosaur species were poorly understood, with competing theories about their ancestral forms.

The newly identified dinosaur species Khankhuuluu mongoliensis is seen in front of three of its evolutionary descendants, including Tyrannosaurus rex (rear) in this handout illustration released on June 11, 2025. Masato Hattori/Handout via REUTERS THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. NO RESALES. NO ARCHIVES.

Though Khankhuuluu shared many traits with tyrannosaurs, it lacked several defining features of the group. Its snout bone was hollow, and the bones surrounding its eyes were different from those of true tyrannosaurs, which had prominent horns and bony ridges. These distinctions place Khankhuuluu just outside the true tyrannosaur family tree, marking it as a transitional species.

Previously, some paleontologists had proposed that long-snouted tyrannosaurs like China’s Qianzhousaurus—nicknamed “Pinocchio-rexes”—represented the ancestral form of the group. However, Khankhuuluu’s anatomy suggests a more complex evolutionary path.

“The tyrannosaur family didn’t follow a straightforward path where they evolved from small size in early species to larger and larger sizes in later species,” Zelenitsky explained.

According to Voris, ancestors of tyrannosaurs originated in Asia and crossed into North America around 85 million years ago via a land bridge connecting Siberia and Alaska. There, they evolved into the giant apex predators like Tyrannosaurus rex. Later, some tyrannosaurs migrated back to Asia, branching into forms like Tarbosaurus and the Pinocchio-rexes.

Ultimately, T. rex dominated western North America until the mass extinction event caused by an asteroid impact 66 million years ago.

“Khankhuuluu was where it all started but it was still only a distant ancestor of T. rex, at nearly 20 million years older,” said Zelenitsky. “Over a dozen tyrannosaur species evolved in the time between them. It was a great-great-great uncle, sort of.”

The discovery of Khankhuuluu mongoliensis offers a vital missing link in understanding how swift, mid-sized predators gradually transformed into some of the largest and most powerful meat-eaters ever to walk the Earth.