A new species of feathered dinosaurs provides hard evidence the prehistoric creatures evolved into birds, a group of Chinese scientists has claimed.
The new dinosaur fossils, disclosed on Friday, representing five different species from two different rock sequences in north-eastern China, all have feathers or feather-like structures.
The new finds are "indisputably" older than archaeopteryx, the oldest known bird, which scientists claim provides exceptional evidence that birds evolved from dinosaurs.
The theory birds evolved from dinosaurs has always been troubled by the absence of feathers more ancient than those on the famous archaeopteryx.
Addressing the annual meeting of the Society of Vertebrate Paleontologists (SVP) in Bristol, Dr Xu Xing, one of the lead scientists behind the discovery, said: "These exceptional fossils provide us with evidence that has been missing until now. Now it all fits neatly into place and we have tied up some of the loose ends."
The oldest bird, archaeopteryx, was older than the feathered dinosaurs previously found. Therefore, critics claimed, feathered dinosaurs could not have been ancestral to birds.
The new feathered species were found in two separate rock formations - the tiaojishan, which would put the fossils at 168 to 151 million years old, and the daohugou formation, which would make them 164 to 158 million years old.
Archaeopteryx lived 150 to 145 million years ago, so was significantly younger than these new dinosaurs, Dr Xing's team said.
One of the dinosaurs, named anchiornis huxleyi, has extensive plumage and profusely feathered feet.
Dr Xing said it had provided important new information on the origins of birds and the evolution of feathers.
He went on: "This fossil provides confirmation that the bird-dinosaur hypothesis is correct and supports the idea that birds descended from theropod dinosaurs, the group of predatory dinosaurs that include allosaurus and velociraptor."