Palaeontologists in China said on Wednesday they had found a bizarre species of giant feathered dinosaur that weighed as much as a car and was related to the Tyrannosaurus rex.

It is by far the biggest feathered dinosaur ever to have been unearthed and raises intriguing questions as to why some of these scaly reptiles developed plumage.

Three nearly complete skeletons of the dino have been uncovered in beds of sediment in Liaoning province, northeastern China, the scientists reported in Nature.

The soil has been dated to around 125 million years ago to the mid-Cretaceous period, at the peak of the dinosaurs' long reign over the planet.

The new species has been named Yutyrannus huali, an amalgam of Latin and Mandarin which means "beautiful feathered tyrant." "The feathers of Yutyrannus were simple filaments," said Xu Xing, a legendary fossil hunter from Beijing's Institute of Vertebrate Palaeontology and Palaeoanthropology.

"They were more like the fuzzy down of a modern baby chick than the stiff plumes of an adult bird."

The fossils include part of the Yutyrannus tail and, most valuably, its skull.

They reveal the sharp teeth, three-fingered hand and pointed head of a typical theropod -- a carnivore that walked on its hind legs.

At adult size, a Yutyrannus would have been about nine meters (30 feet) long and weighed around 1.4 tons (3,000 pounds), with feathers at least 15 centimeters (six inches) long.

That makes it a midget compared to its cousin T. rex but a giant compared to the Beipiaosaurus, the previous plumed record-breaker, which was 40 times lighter.

Yutyrannus was too big to fly and in any case the feathers were too downy to even get it off the ground, says the paper.

That raises the theory that the feathers evolved for insulation at what was an unusually cool time of the long Cretaceous era.

But another idea is that the feathers were there for display, as birds use them for mating purposes.

The nearly complete skeletons came from the Yixian Formation in Liaoning, which has been a treasure trove of dinosaurs.

Discoveries there have bolstered the theory that birds today are the descendants of small feathered theropods that took to the trees, either for food or safety, and then learned to glide or fly.

"Yutyrannus dramatically increases the size range of dinosaurs for which we have definite evidence of feathers," Xu said.

"It's possible that feathers were much more widespread, at least among the meat-eating dinosaurs, than most scientists would have guessed even a few years ago." (AFP)