New species of dinosaur discovered that 'rewrites' T.rex family tree
Scientists have discovered a new species of dinosaur - in the collection of a Mongolian museum - that they say "rewrites" the evolutionary history of tyrannosaurs.
Researchers concluded that two 86 million-year-old skeletons they studied belonged to a species that is now the closest known ancestor of all tyrannosaurs - the group of predators that includes the iconic T.rex.
The researchers named the species Khankhuuluu (pronounced khan-KOO-loo) mongoliensis, meaning Dragon Prince of Mongolia.
The discovery, published in Nature, is a window into how tyrannosaurs evolved to become powerful predators that terrorised North America and Asia until the end of the reign of the dinosaurs.
"'Prince' refers to this being an early, smaller tyrannosauroid," explained Prof Darla Zelenitsky, a palaeontologist from the University of Calgary in Canada. Tyrannosauroids are the superfamily of carnivorous dinosaurs that walked on two legs.
The first tyrannosauroids though were tiny.
PhD student Jared Voris, who led the research with Prof Zelenitsky, explained: "They were these really small, fleet-footed predators that lived in the shadows of other apex predatory dinosaurs."
Khankhuuluu represents an evolutionary shift - from those small hunters that scampered around during the Jurassic period - to the formidable giants, including T-rex.
It would have weighed about 750kg, while an adult T.rex could have weighed as much as eight times that, so "this is a transitional [fossil]," explained Prof Zelenitsky, "between earlier ancestors and the mighty tyrannosaurs".
"It has helped us revise the tyrannosaur family tree and rewrite what we know about the evolution of tyrannosaurs," she added.
The new species also shows early evolutionary stages of features that were key to the tyrannosaurs' tyranny, including skull anatomy that gave it a strong jaw. Jared Voris explained: "We see features in its nasal bone that eventually gave tyrannosaurs those very powerful bite forces."
The evolution of such powerful jaws allowed T-rex to pounce on larger prey, and even bite through bone.
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The two partial skeletons that the team examined in this study were first discovered in Mongolia back in the early 1970s. They were initially assigned to an existing species, known as Alectrosaurus, but when Mr Voris examined them, he identified the Tyrannosaur-like features that set it apart.
"I remember getting a text from him - that he thought this was a new species," recalled Prof Zelenitsky.
The fact that this group of dinosaurs were able to move between North America and Asia - via land bridges that connected Siberia and Alaska at the time - also helped them to find and occupy different niches.
Mr Voris explained: "That movement back and forth between the continents basically pushed the evolution of different tyrannosaur groups" over millions of years.
Prof Zelinitsky added: "This discovery shows us that, before tyrannosaurs became the kings, they were they were princes."
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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. 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Khankhuuluu mongoliensis was slender with features like no other member of the tyrannosaur family tree. This illustration depicts how the slender Khankhuuluu mongoliensis may have appeared as it roamed Mongolia during the Cretaceous period. The newest addition to the tyrannosaur family, the discovery of this "dragon prince from Mongolia" sheds light on the origins of Tyrannosaurus rex. Illustration by Julius Csotonyi Tyrannosaurus rex is a carnivorous icon. Exceeding 40 feet in length and nine tons, the bone-crushing giant stands out as the largest and last of its meat-eating family. Now a new and far smaller tyrannosaur is filling in the famous dinosaur's evolutionary backstory. The newest addition to the tyrannosaur family tree is named Khankhuuluu mongoliensis, which translates to 'dragon prince from Mongolia.' 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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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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. 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