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The babies of a ferocious group of meat-eating dinosaurs, that included T-rex, were huge, fully toothed and clawed and “born ready” to kill, according to analysis of recently uncovered embryonic remains.
The fossils are from two species in the group called tyrannosaurs, the apex predators in Asia and North America during the Cretaceous Period toward the end of the dinosaur age.
The remains consist of a 3cm-long, 77 million-year-old jaw bone found in Montana that may have belonged to a species called Daspletosaurus and a roughly 72-million-year-old claw unearthed in Canada’s Alberta province that probably came from an Albertosaurus.
Both were slightly smaller cousins of the largest-known tyrannosaur, the Tyrannosaurus-rex, which was more than 12 metres (40ft) long and weighed around seven tonnes.
The fossils indicated that these were bigger than any other known dinosaur babies – one metre (3ft) long, or the size of a medium dog – and hatched from what must have been enormous eggs, perhaps exceeding the 43cm (17inch) length of the largest dinosaur eggs currently known.
The jaw possesses distinctive tyrannosaur traits, including a deep groove inside and a prominent chin.
University of Edinburgh paleontologist Greg Funston, lead author of the research published in the Canadian Journal of Earth Sciences, said the scientists were amazed at how similar the embryonic bones were to older juvenile and adult tyrannosaurs and noted that the jaws boasted functional teeth.
“So although we can’t get a complete picture, what we can see looks very similar to the adults,” Funston said.
It appears that tyrannosaurs, Funston added, were “born ready to hunt, already possessing some of the key adaptations that gave tyrannosaurs their powerful bites.
“So it’s likely that they were capable of hunting fairly quickly after birth, but we need more fossils to tell exactly how fast that was.”
