A "shaggy" close cousin of Tyrannosaurus rex discovered in China is the biggest feathered dinosaur known, scientists have revealed.
Yutyrannus huali measured almost 30 feet and weighed more than a tonne. Like T. rex it was a formidable predator, but - unlike its famous relative - was covered in downy feathers.
Scientists believe the feathers had no connection with flight and would have been used to keep the animal warm.
Despite being dwarfed by T. rex, Yutyrannus was 40 times heavier than the largest feathered dinosaur known to date, Beipiaosaurus.
Three almost complete fossil skeletons of Yutyrannus, one adult and two juveniles, were found in Liaoning Province, north east China.
Its name is a combination of Latin and Mandarin meaning "beautiful feathered tyrant".
Isolated patches of preserved skin from T. rex suggest that it was covered in scales rather than feathers.
But Yutyrannus, which like T. rex walked on two legs, showed clear evidence of primitive plumage.
"The feathers of Yutyrannus were simple filaments," said Professor Xu Xing, from the Chinese Academy of Sciences in Beijing, whose team described the find in the journal Nature. "They were more like the fuzzy down of a modern baby chick than the stiff plumes of an adult bird."
T. rex lived in the warm Late Cretaceous period, which ended when the dinosaurs went extinct 65 million years ago.
Yutyrannus, on the other hand, dates back to the cooler Early Cretaceous. Its feathers probably provided insulation, despite the animal's large size, scientists believe.
"The idea that primitive feathers could have been for insulation rather than flight has been around for a long time," said co-author Dr Corwin Sullivan, a Canadian palaeontologist based at the Chinese Academy of Sciences.
"However, large-bodied animals typically can retain heat quite easily, and actually have more of a potential problem with overheating. That makes Yutyrannus, which is large and downright shaggy, a bit of a surprise."
Prof Xu said Yutyrannus dramatically increased the size range of feathered dinosaurs.
He added: "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."