An early cousin of the tyrannosaurus grew to the size of a bus but was covered in fur-like feathers like those found on chickens, according to fossils unearthed by palaeontologists in northeast China.
Weighing about 1 1/2 tonnes and standing 10 metres high, it is probably the largest feathered animal, living or extinct, yet discovered. Scientists say the predator made kills in the snow.
In an article published in British science magazine Nature, palaeontologist Xu Xing and his team from the Institute of Vertebrate Palaeontology and Palaeoanthropology at the Chinese Academy of Sciences in Beijing described three nearly perfect fossils of a previously unknown species they found in Batuyingzi village in Beipiao, Liaoning province.
The dinosaurs were named Yutyrannus huali, or 'beautiful feathered tyrant'.
With big heads, powerful jaws and three fingers on hand-like forelegs, they belonged to the family of tyrannosauroids.
But 'most significant, Y. huali bears long filamentous feathers, thus providing direct evidence for the presence of extensively feathered gigantic dinosaurs', the researchers wrote.
Xu said the feathers not only looked like the coat of a chicken, they functioned similarly.
'The feathers covered the whole body, likely providing heat insulation against cold weather,' he said. 'You know, they lived in the early Cretaceous period. It was an ice age.'
A closer examination of the fossilised imprints of the feathers suggested neither shortness nor softness. The feathers' measured lengths were at least 15cm, with relatively robust bony structures.
So scientists guessed that the feathers might have served another purpose - showing off. 'We highly suspect that these feathers may have had colours to attract mating partners, and we have launched a study on the topic,' Xu said.
Chemical residuals of pigments and their geometric arrangement will be sought under electron microscopes for clues. Using the method, Chinese scientists have already reproduced colours on the feathers of some smaller, bird-like dinosaurs.
'If lucky, a colourful tyrannosauroid can be reproduced with similar methods, too,' Xu said.
Palaeontologists long believed that dinosaurs shed their feathers as they grew in size. The larger an animal grew, the more heat would be trapped in a furry cover.
'Feather is a curse in a tropical forest but these furry giants needed to deal with some really cold winters, and the fur was a blessing,' Xu said.
The tyrannosauroids became dominant large predators in the middle to early Cretaceous ecosystems of northeastern China - a period so cold that forests were covered in thick snow during winter as they are today.
The size of a bus, Y. huali must have developed ways to combat the freezing climate, and fur could have been one of them, Xu said.
The scientists also believe that the Y. huali lived in groups, judging by their gravesites. But like their famous cousin tyrannosaurus rex, they may have hunted alone.
The feathered carnivore may have crouched in the snow, waiting behind bushes and trees, for prey to approach, Xu said. They would grab the prey using forelegs and tear them apart with a powerful jaw, he said.
The surprisingly huge size of Y. huali and their feathers suggest that, after more than a century of digging and studying, our understanding of dinosaurs remains limited, if not erroneous, Xu said.
'Long-held beliefs have been frequently toppled by recent findings,' he said.
A preservation environment for fossils has turned Beipiao into a holy site for palaeontologists.
Volcano lakes were formed before the time of the dinosaurs. The volcanoes later erupted again and again, burying the dinosaurs, as well as other animals and plants, under many layers of fine ash that preserved fine details in fossils.
More than 99 per cent of dinosaur fossils with feathers have been found on the mainland, according to Xu.