New dinosaur fossils found in Siberia have "completely changed our vision of dinosaurs", scientists have said.
The fossils prove that dinosaurs were likely covered entirely in feathers or had the possibility to grow feathers, in stark contrast to common interpretations of what dinosaurs looked like.
The 150 million year-old fossils discovered in Russia are from a group of plant-eating dinosaurs called omnithischians, which account for half of all dinosaurs.
Until now, fossilised evidence of feathery or 'fluffy' dinosaurs has come exclusively from China and from a meat-eating group of creatures called theropods.
The find takes the origin of feathers millions of years further back in time than has been thought in the past.
The findings have been compiled in a new study published in the journal Science on Friday.
Dr Pascal Godefroit of the Royal Belgian Insititute of Natural Sciences in Brussels, Belgium led the research. He said the discovery has been a "big surprise".
"The fact that feathers have now been discovered in two distinct groups, theropods in China and ornithischians in Russia, means that the common ancestor of these species which might have existed 220 million years ago also probably had feathers."
The discovery has "completely changed our vision of dinosaurs", he added.
"Instead of thinking of dinosaurs as dry, scary scaly creatures a lot of them actually had a fluffy, downy covering like feathers on a chick," said co-researcher Dr Maria McNamara of Cork University in Ireland.