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While Tyrannosaurus rex is the most famous dinosaur, its true evolutionary story has remained incomplete—until now. In June 2025, a team of paleontologists from the University of Calgary published a landmark paper in Nature announcing the discovery of Khankhuuluu mongoliensis, a species that rewrites the ancestry and migration of the tyrannosaurs.
The fossils, which had been stored in a Mongolian museum for four decades, were initially misidentified. A fresh analysis revealed that they belong to a previously unknown species, aptly named “dragon prince of Mongolia.” Khankhuuluu is the closest known ancestor of all tyrannosaurids, including the iconic T. rex.
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Unlike modern tyrannosaurids, Khankhuuluu is an older member of the broader clade Tyrannosauroidea. Radiometric dating places the species at roughly 86 million years ago, about 10–20 million years before the Late Cretaceous giants such as T. rex and Tarbosaurus. Though not the oldest tyrannosauroid—those trace back to the Middle Jurassic—Khankhuuluu fills a critical gap just as tyrannosauroids rose to apex‑predator status.
In size, Khankhuuluu was substantial for its time, measuring about 13 feet (4 m) in length and weighing around 1,650 pounds (750 kg). By comparison, a mature T. rex could reach 13,000 pounds (6,000 kg). Its jaws were shallower, indicating a weaker bite force, and the cranial bones surrounding the snout and eyes show subtle structural differences. One shared trait with its descendants is the presence of tiny forelimbs.
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Beyond biology, the geographic origin of Khankhuuluu challenges previous assumptions about tyrannosaur dispersal. Fossils of tyrannosaurids have been found in both North America and Asia, yet the route of their spread remained uncertain. At the time of Khankhuuluu, western North America (Laramidia) was separated from Asia by the Bering Strait, which later became a land bridge.
Researchers now posit that Khankhuuluu was the first tyrannosauroid to traverse this bridge, carrying the lineage into Laramidia. Subsequent migrations—first back into Asia around 78 million years ago and then again into North America—led to the diversification of two lineages: one small, horned group, and one larger, bone‑crushing lineage that ultimately produced T. rex.
These insights not only deepen our knowledge of tyrannosaur evolution but also highlight Asia’s pivotal role in shaping the family’s history—a factor previously underestimated.
