The father of T. rex: Asian, small, and quick-footed

BarcelonaVery agile, but of medium size and with small horns that served to match or intimidate opponents. This was the Khankhuuluu –the prince of dragons, in Mongolian–, a new species of dinosaur considered the most recent ancestor of the giant tyrannosaurs and which paleontologists from the Faculty of Science at the University of Calgary have just discovered. In a publication in the journal NatureResearchers have described how this lineage of predators evolved after the extinction of other large predatory dinosaurs around 85 million years ago, providing further insight into the evolution of tyrannosaurs.

Led by Jared Voris and Darla Zelenitsky, the research finds that the Khankhuuluu was the closest ancestor of the giants famously depicted in Jurassic Park, the tyrannosaurs. "This new species gives us a window into the ascending stage of tyrannosaur evolution—right when they're transitioning from small predators to their apex predator form," says Voris. That is, the carnivorous animal species that dominates the rest in an ecosystem over a period of time. In fact, it predates the iconic—and feared— Tyrannosaurus rex (T. rex).

He Khankhuuluu is the last known ancestor of tyrannosaurs found in the Asian fossil record. According to the researchers, this predator shared many characteristics with its tyrannosaur descendants, but it was missing some of the most defining ones. For example, its size: this rediscovered species weighed 750 kilograms (about the same as a horse) and was about 4 meters long. It was therefore two to three times smaller than its enormous descendants, which weighed up to 8,000 kg.

Furthermore, this dinosaur had a long, shallow skull, which shows that it did not have the bone-crunching ability that the T. rex, always characterized as a species with large, sharp teeth and gigantic bodies. On the other hand, the Khankhuuluu It wasn't known for its aggressiveness (although it's not possible to rule out that it was), but rather for its speed. It had quick feet that made it easy to surprise its prey when hunting.

The conclusions come from the study of two partial skeletons identified in the Bayanshiree geological formation in the Gobi Desert, Mongolia, which had been studied in the 1970s by Altangerel Perle. This Mongolian paleontologist then compared the fossils with those of another medium-sized tyrannosaur called Alectrosaurus from ChinaUntil 2023, when Voris became interested, the remains were kept at the Institute of Paleontology of the Mongolian Academy of Sciences.

Migration from Asia to the U.S.

Using computer models, researchers identified the migratory patterns of this species. "The Khankhuuluu, or a closely related species, may have immigrated to North America from Asia about 85 million years ago," said Zelenitsky, a paleontologist and associate professor in the Department of Earth, Energy and Environment.

The study's results show that tyrannosaur movement back and forth between Asia and North America was less frequent and less sporadic than previously known. Specifically, the research reveals that the new species, or one of its relatives, traveled across a land bridge to the Americas. tyrannosaurs.

The fossil record indicates that tyrannosaurs were exclusive to North America for several million years before immigrating to Asia, where the lineage split into two groups. T. rex, and the other group evolved into a medium-sized, long-snouted species called Pinocchio Rex, which until the discovery of the Khankhuuluu It was considered the species closest to the tyrannosaurs.