Their parents may have wielded their massive strength and size to kill large prey, but young tyrannosaurs were careful predators who relied on quickness and agility rather than raw power, scientists have found.

Tyrannosaurs were the largest ever known dinosaurs that roamed the earth some 65 million years ago.

An international team of scientists who investigated the youngest and most complete skull of a 70-million—year-old tyrannosaur, unearthed five years ago in the Gobi Desert in Mongolia, believe the young animals were not powerful like their parents and fed on smaller preys.

The skull was found as part of a nearly complete skeleton, missing only the neck and two-thirds of the tail, which belonged to a Tarbosaurus, a fearsome predator roughly as large as its closest known relative, Tyrannosaurs rex.

“We knew that adult Tarbosaurus were a lot like T rex,” researcher Takanobu Tsuihiji, of the National Museum of Nature and Science in Tokyo, was quoted as saying by LiveScience.

Based on careful analysis of the microstructure of the leg bones, researchers estimated this predator was only 2 to 3 years old when it died.

It was about 9 feet long, about 3 feet high at the hip and weighed about 32 kg. In comparison, an adult Tarbosaurus was 35 to 40 feet long, 15 feet high, weighed about 6 tons and probably had a life expectancy of about 25 years.

CAT scans of the immature 11.4-inch skull revealed that it was far more delicate than an adult’s and was incapable of handling the kinds of twisting and stress that the reinforced skull of a grown-up Tarbosaurus could.

“Adults show features throughout the skull associated with a powerful bite — large muscle attachments, bony buttresses, specialised teeth,” Tsuihiji explained.

In comparison, “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.”

This suggests “the younger animals would have taken smaller prey that they could subdue without risking damage to their skulls,” Tsuihiji explained.

“This spectacular specimen provides us with a really clear window into how these dinosaurs changed over the course of their lives,” Witmer told LiveScience.

“Tarbosaurus is found in the same rocks as giant dinosaurs like the long-necked sauropod Opisthocoelicaudia and the duckbill hadrosaur Saurolophus,” said researcher Mahito Watabe of the Hayashibara Museum of Natural Sciences in Okayama, who led the expedition that uncovered the new skull.

“But the young juvenile Tarbosaurus would have hunted smaller prey, perhaps something like the bony-headed dinosaur Prenocephale.”

This range of feeding strategies could have been one of the secrets of success for tyrannosaurs, strengthening their role as the dominant predators during their time, Witmer said.

The scientists detailed their findings in the Journal of Vertebrate Paleontology.

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