The discovery of the new bird-like dinosaur from the Jurassic period, dubbed Eosinopteryx, presents a challenge to widely accepted theories on the origin of flight, they said.
"This discovery sheds further doubt on the theory that the famous fossil Archaeopteryx -- or 'first bird' as it is sometimes referred to -- was pivotal in the evolution of modern birds," said Gareth Dyke of the University of Southampton, who is based at the National Oceanography Center, Southampton.
Rather than Archaeopteryx, paleontologists have come to believe birds evolved from a group of dinosaurs called theropods from the Early Cretaceous period of Earth's history, around 120 million to 130 million years ago.
The new "bird-dinosaur" Eosinopteryx is additional evidence of this, researchers said.
The fossilized remains found in northeastern China suggest Eosinopteryx, while feathered, was a flightless dinosaur with a small wingspan and a bone structure that would have restricted its ability to flap its wings.
It had toes suited to walking along the ground, researchers said, and fewer feathers on its tail and lower legs, which would have made it easier to run.
"Our findings suggest that the origin of flight was much more complex than previously thought," Dyke said in a university release Thursday.