New Tyrannosaur species reshapes T. rex family tree
A newly identified dinosaur species from Mongolia is rewriting the history of the T. rex family tree.
Dubbed the 'Dragon Prince' (scientifically named Khankhuuluu mongoliensis), this prehistoric predator lived about 86 million years ago and is believed to be a key ancestor of the famous Tyrannosaurus rex.
For decades, fossils of this dinosaur sat largely overlooked in museum collections, misidentified as a known species called Alectrosaurus. But recent re-examination by researchers revealed that the fossils represent a completely new species — one that provides a vital missing link between smaller early tyrannosaurs and the massive apex predators that later dominated Earth.
At about 13 feet long and weighing about 1,650 pounds, the Dragon Prince was much smaller than later tyrannosaurs like T. rex, which could grow up to 41 feet long and weigh more than 23,000 pounds. It had a smaller head and longer arms compared to its gigantic descendants, meaning it may have occupied an in-between evolutionary phase.
Scientists say the discovery fills a crucial gap in understanding how tyrannosaurs evolved from modest-sized hunters to colossal rulers of their ecosystems. Paleontologists believe the Dragon Prince primarily hunted prey smaller than itself, unlike later giants that tackled enormous herbivores.
Beyond its size and anatomy, experts say the find offers fresh insights into tyrannosaur migration patterns. Research shows that around 85 million years ago, a species closely related to K. mongoliensis migrated from Asia to North America across a land bridge near today's Bering Strait.
This migration likely gave rise to the first true tyrannosaurs in North America, which went on to become dominant predators of the Late Cretaceous period.
Later migrations back and forth between Asia and North America helped shape tyrannosaur diversity, producing both massive species like Tarbosaurus bataar and smaller, slimmer ones like Qianzhousaurus sinensis, nicknamed 'Pinocchio rex.' About 68 million years ago, one giant tyrannosaur species likely migrated back to North America and evolved into T. rex.
This discovery, published in Nature, highlights how migration events fueled tyrannosaur evolution and offers a fascinating glimpse into the complex family tree of these iconic dinosaurs — the princes before they became kings.
Copyright 2025 Nexstar Media, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
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Comparing the fossils of mature Khankhuuluu (a, d, g) with fossils of mature Gorgosaurus (c, f, i) and juvenile Gorgosaurus (b, e, h) provides new insights into the evolutionary lineage between the smaller-bodied tyrannosauroids, such as Khankhuuluu, and the larger eutyrannosaurians like Gorgosaurus and Tyrannosaurus. Silhouettes compare the sizes of Khankhuuluu (left) with a juvenile (right) and adult (middle) Gorgosaurus. Scale bars, 5 cm (individual elements) and 1 m (silhouette). Illustration by Voris et al. (2025), Nature In the early 1970s, Mongolian paleontologist Altangerel Perle found a pair of partial tyrannosaur skeletons in the eastern part of the country. The bones seemed similar to a small tyrannosaur that had been named before, Alectrosaurus. But when University of Calgary paleontologist and study co-author Jared Voris studied the bones during a research trip to Mongolia in 2023, he soon realized that the bones did not belong to Alectrosaurus at all. The bones from the two skeletons belonged to a new form of tyrannosaur that had been waiting to be discovered in collections for half a century. 'It had features like a hollow air chamber in side its nasal bone, which no other tyrannosaur species has,' Voris says. The fossils deserved a new name and have been recategorized as Khankhuuluu. Voris has found tyrannosaurs hiding in plain sight before. In 2020, Voris and colleagues named the 80 million-year-old tyrannosaur Thanatotheristes from bones assigned to another species found in Alberta. ("Reaper of Death" tyrannosaur discovered in Canada.) The finds are part of a burgeoning array of tyrannosaur discoveries. Instead of a simple line of evolution from early tyrannosaurs to T. rex, paleontologists have uncovered a wildly branching evolutionary bush of different tyrannosaur subgroups that came and went through the Cretaceous. 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Sometime around the time of Khankhuuluu, Voris and colleagues propose, such small, slender tyrannosaurs were dispersing from prehistoric Asia into North America over a land bridge. 'Tyrannosaurs evolved into those giant apex predators and diversified very rapidly across North America,' Voris says, the first of what Zelenitsky calls 'two explosions of tyrannosaurs.' Some of the predators remained slender and chased smaller prey while others became bulkier and hunted larger dinosaurs, and they roamed habitats from southern California to New Jersey. (See how these fierce dinos evolved in our pages over 100 years.) The new study suggests, however, that the direct ancestors of T. rex, did not evolve in North America. Voris and colleagues propose that around 79 and 78 million years ago at least one lineage of tyrannosaurs ventured back into Asia. The researchers know this because of the close relationship of two tyrannosaur groups that at a glance might seem very different. When tyrannosaurs returned to Asia during this period and underwent their second explosion, one group was relatively slender and had long snouts decorated with small horns, like the 'Pinocchio' dinosaur Qianzhousaurus. The other group began to grow larger, with deep skulls adept at crushing bones, like Tarbosaurus. T. rex evolved from ancestors in the second group, a lineage of bone-crushers that once again crossed the land bridge back into North America between 73 and 67 million years ago—making T. rex a new form of predator that arrived from another continent. 'The new analysis provides strong support that the ancestors of T. rex evolved from a group of tyrannosaurs that ventured back to Asia after they had undergone an evolutionary radiation in North America,' Morrison says. Ultimately, the study suggests that the rise of one of Earth's largest carnivores was due to a back-and-forth between North America and Asia that took place over a period of 20 million years. Had a devastating asteroid impact not abruptly ended the Cretaceous 66 million years ago, tyrannosaurs would have undoubtedly kept changing.
