Discovery of Khankhuuluu mongoliensis: A Precursor to T. rex Unveiled

In a groundbreaking study, paleontologists have uncovered a significant precursor to the Tyrannosaurus rex, named Khankhuuluu mongoliensis, which lived approximately 86 million years ago during the Cretaceous Period. This discovery, made in Mongolia, predates T. rex by about 20 million years, providing crucial insights into the evolutionary lineage of one of the most iconic predators in history.

According to Dr. Darla Zelenitsky, a paleontologist at the University of Calgary and co-author of the study published in the journal Nature on June 11, 2025, "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." Khankhuuluu mongoliensis, translating to "Dragon Prince" in Mongolian, measures approximately 13 feet (4 meters) in length and weighs around 1,600 pounds (750 kilograms), making it considerably smaller than its later descendant, T. rex, which could exceed lengths of 40 feet (12.3 meters).

The fossils of Khankhuuluu, excavated during the 1970s, include parts of the skull, limbs, tail, and back bones, but were only recently fully analyzed. This has allowed researchers to gain a more comprehensive understanding of tyrannosaur evolution. Jared Voris, a doctoral student at the University of Calgary and the study's lead author, remarked, "What started as the discovery of a new species ended up with us rewriting the family history of tyrannosaurs."

Previously, paleontologists struggled to delineate the relationships among various species within the tyrannosaur family. The findings from Khankhuuluu suggest a more intricate evolutionary history than previously understood.

In examining the anatomical features of Khankhuuluu, researchers noted that it shared several traits with tyrannosaurs but also exhibited distinct differences. Its hollow snout bone and unique eye socket structure set it apart from true tyrannosaurs, which are characterized by prominent horns and bony ridges. This places Khankhuuluu just outside the true tyrannosaur family tree, marking it as a transitional species. Dr. Zelenitsky elaborated, "The tyrannosaur family didn't follow a straightforward path where they evolved from small size in early species to larger sizes in later species."

The evolutionary journey of the tyrannosaur lineage is believed to have begun in Asia, with ancestors migrating to North America around 85 million years ago, facilitated by a land bridge connecting Siberia and Alaska. There, they evolved into larger apex predators like T. rex. Subsequent migrations back to Asia resulted in the emergence of forms such as Tarbosaurus and other smaller tyrannosaurs.

Despite its size and agility, Khankhuuluu was likely a swift hunter, preying on smaller creatures such as bird-like dinosaurs, including oviraptorosaurs and ornithomimosaurs. Its sharp, knife-like teeth were adapted for slashing rather than crushing prey, further highlighting its unique ecological niche.

The discovery of Khankhuuluu mongoliensis not only enhances understanding of tyrannosaur evolution but also emphasizes the diversity of predatory forms that existed prior to the reign of T. rex. As noted by Voris, "Khankhuuluu was where it all started but it was still only a distant ancestor of T. rex, at nearly 20 million years older. Over a dozen tyrannosaur species evolved in the time between them. It was a great-great-great uncle, sort of." This research underscores the complexity of dinosaur evolution and the importance of continued paleontological exploration in uncovering the history of life on Earth.