Mini T-Rex fossil found in China

The skull of the Raptorex is dwarfed by that of 'Sue', a famous adult T-Rex at the Field Museum in Chicago. -- PHOTO: AGENCE FRANCE-PRESSE

CHICAGO: A pint-sized version of the Tyrannosaurus rex, with similarly powerful legs, razor-sharp teeth and tiny arms, roamed China some 125million years ago, say scientists, startled by the discovery.

The new animal, based on a single fossil smuggled out of China and eventually sold to a private collector, has been named Raptorex which means 'king raptor'. It lived in a lake-dotted region of northern China.

Measuring a mere 3m, the Raptorex weighed only about 60kg and was nearly 100 times smaller than the king of the dinosaurs, according to a paper published on Thursday in the online version of the journal Science.

This scrambles the picture of mega-predator evolution and raises the question of whether other jumbo dinosaurs had budget-sized versions.

The orthodoxy in palaeontology has been that T-Rex got its peculiar body shape - the colossal head, powerful jaws and comically short forelimbs - as a side-effect of evolving into a giant animal. The small arms have been seen as a natural trade-off for the big head.

'What we're looking at is a blueprint for a fast-running set of jaws,' University of Chicago palaeontologist Paul Sereno, the lead author of the Science paper, said this week. The blueprint works at multiple scales and across tens of millions of years of the Mesozoic era, he added.

The Raptorex fossil shows that the skinny arms evolved, not in order to help it offset a heavier overall bodyweight, but as a trade-off for agility and speed.

The tyrannosaurus genus did not reach its full size until about 85million years ago and was wiped out about 65million years ago. This suggests that for most of their evolutionary history, tyrannosauruses were small animals that lived in the shadow of other very large dinosaur predators.

The new species will be named Raptorex Kriegsteini, in honour of American eye surgeon and dinosaur enthusiast Henry Kriegstein, who bought the fossil and the dinosaur's link to raptors and the T-Rex.

AGENCE FRANCE-PRESSE, LOS ANGELES TIMES-WASHINGTON POST, WASHINGTON POST