Carnivorous baby dinosaurs were born with teeth and 'ready to hunt', scientists find

 

A baby tyrannosaur from the Cretaceous Period of North America, based on partial fossils unearthed in the US. (Reuters: Julius Csotonyi)

Silhouettes of two baby tyrannosaurs based on partial fossils unearthed in the US state of Montana and in the Canadian province of Alberta.(Reuters: Greg Funston/University of Edinburgh)

Scientists for the first time have found embryonic remains from a group of ferocious meat-eating dinosaurs that includes the Tyrannosaurus rex.

They found fossilised jaw and claw bones that show these record-size babies looked a lot like adults and were "born ready" to hunt.

The fossils, the researchers said, represented two species from the tyrannosaurs group, the apex predators in Asia and North America during the Cretaceous Period toward the end of the dinosaur age.

The bones indicated these were bigger than any other known dinosaur babies — 1 metre long, or the size of a medium dog — and hatched from what must have been enormous eggs, perhaps exceeding the 43-centimetres in length of the largest dinosaur eggs currently known.

University of Edinburgh palaeontologist 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.

He also 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," Mr Funston said.

He added it appears that tyrannosaurs were "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," he said.

The roughly 77 million-year-old jawbone, about 3 centimetres in length, was unearthed in the US state of Montana, and may belong to a species called Daspletosaurus.

The roughly 72 million-year-old wedge-shaped claw came from Canada's Alberta province and may belong to a species called Albertosaurus.

Both are slightly smaller cousins of Tyrannosaurus rex. The largest-known tyrannosaurs topped 12 meters-long and 8 tonnes in weight.

However, the jaw possesses distinctive tyrannosaur traits, including a deep groove inside and a prominent chin.

Reuters