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Science

Younger Tyrannosaurs Relied on Speed not Power for Food

Skull of a 2-year-old juvenile Tarbosaurus, a Cretaceous tyrannosaur from Mongolia, with an adult skull at right and a teenage skull behind for comparison. Courtesy of WitmerLab at Ohio University.

Younger tyrannosaurs and similarly built species of dinosaur probably relied on speed and agility, rather than sheer power like their parents, to find their food.

This is the result of a new study which analysed the youngest and most complete known skull for any species of tyrannosaur, a 70 million year old skull which comes from a Mongolian dinosaur species known as Tarbosaurus bataar, the closest known relative of the infamous T. rex.

A newly discovered specimen of the Mongolian tyrannosaur Tarbosaurus comes from a juvenile only 2-3 years old when it died, providing insight into the growth and changing lifestyles of tyrannosaurs.
Animation by Ridgely and Witmer, Courtesy of WitmerLab at Ohio University.

“It’s one of the secrets of success for tyrannosaurs—the different age groups weren’t competing with each other for food because their diets shifted as they grew,” said Ohio University paleontologist Lawrence Witmer.

The analysis was published in the Journal of Vertebrate Palaeontology, and and revealed changes in the 11.4-inch skull that suggests the younger dinosaur would have had a much different lifestyle than its parent. The analysis showed that the juvenile was probably only 2 to 3 years old when it died, measured in at 9 feet in total length, and was about 3 feet high at the hip and weighed about 70 pounds.

“We knew that adult Tarbosaurus were a lot like T. rex,” said lead author Takanobu Tsuihiji, a former Ohio University postdoctoral fellow who is now a postdoctoral researcher at the National Museum of Nature and Science in Tokyo. “Adults show features throughout the skull associated with a powerful bite…large muscle attachments, bony buttresses, specialized teeth. The juvenile is so young that it doesn’t really have any of these features yet, and so it must have been feeding quite differently from its parents.”

“This little guy may have been only 2 or 3, but it was no toddler…although it does give new meaning to the phrase ‘terrible twos,’” said Witmer, Chang Professor of Paleontology at the Ohio University College of Osteopathic Medicine. “We don’t know to what extent its parents were bringing it food, and so it was probably already a pretty capable hunter. Its skull wasn’t as strong as the adult’s, and would have had to have been a more careful hunter, using quickness and agility rather than raw power.”

This is a fascinating look into a species long since gone from our planet, and a revelation which helps shed light on just how the tyrannosaurus was so powerful and at the top of the food chain. With different hunting strategies – the younger ones going for smaller prey which required agility and speed to catch, the adults targeting larger prey that required strength to bring down – the tyrannosaurus was able to stay on top of the food pyramid its entire life. Additionally, there would have been lots of food for both junior and parent, in the time and place where they lived.

“The juvenile skull shows that there must have a change in dietary niches as the animals got older,” Tsuihiji said. “The younger animals would have taken smaller prey that they could subdue without risking damage to their skulls, whereas the older animals and adults had progressively stronger skulls that would have allowed taking larger, more dangerous prey.”

Silhouettes of an adult Tarbosaurus and the newly discovered juvenile, along with a human for scale. Courtesy of the Hayashibara Museum of Natural Sciences.

“Tarbosaurus is found in the same rocks as giant herbivorous dinosaurs like the long-necked sauropod Opisthocoelicaudia and the duckbill hadrosaur Saurolophus,” said Mahito Watabe of the Hayashibara Museum of Natural Sciences in Okayama, who led the expedition to Mongolia in 2006 that uncovered the new skull. “But the young juvenile Tarbosaurus would have hunted smaller prey, perhaps something like the bony-headed dinosaur Prenocephale.”

Animation of the skull of a newly discovered juvenile specimen of the Mongolian tyrannosaurTarbosaurus with the bones and some other anatomical structures labeled. The juvenile was only 2-3 years old when it died, providing insight into the growth and changing lifestyles of tyrannosaurs.
Animation by Ridgely and Witmer, Courtesy of WitmerLab at Ohio University.

Source: Ohio University




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