Two fossils showing evidence of feathers have been dated to 130 million years ago, pushing the beginnings of bird evolution back by a least 5 million years, paleontologists say.
The fossils found in China are of the earliest known member of the group known as Ornithuromorpha, which would eventually give rise to Neonithes - modern birds.
The small birds, from the area that would become northeastern China, were probably wading birds resembling modern shorebirds but were likely capable of agile flight, the researchers say.
Dubbed Archaeornithura meemannae, the two fossil specimens were unearthed in China's Hebei province. The previous oldest known example of Ornithuromorpha lived about 125 million years ago.
"The new fossil represents the oldest record (about 130.7 million years ago) of Ornithuromorpha," says study co-author Wang Min of the Chinese Academy of Sciences.
It has more in common with a modern bird than any other fossil found from such an early stage in bird evolution, he says.
"The new bird is quite derived and has many advanced features of modern birds, and thus is far away from the transitional history of dinosaurs-birds," says Wang.
The fact that A. meemannae is more bird-like than even some later members of Ornithuromorpha suggest they may have an older-yet ancestor in common that so far hasn't been identified.
"The most primitive bird of Ornithuromorpha is most likely from older deposits than what we discovered now," Wang says.
The well-preserved fossils showed the early bird was about 6 inches tall; the lack of feathers on its legs, even in their upper regions, leads the scientists to suggest it spent a lot of time wading in the water.
It likely lived near the shores of lakes, looking for insects and other small prey, a lifestyle similar to what is seen in modern long-legged birds such as herons and cranes, they note.
However, they added, the size and shape of its wing bones suggest these birds were capable of good maneuverability in the air.
Birds started to evolve from the dinosaurs around 150 million years ago toward the end of the Jurassic period.
This is the period of Archaeopteryx, still the oldest and most primitive known bird, but since it has no living descendants it is generally considered more as a feathered dinosaur without direct links to today's modern birds, says study senior author Zhonghe Zhou. The study was published in the journal Nature Communications.
A. meemannae and some of its relatives did survive, in contrast, providing a direct evolutionary link to modern birds, he says.
"These birds had a lot of advantages ... better flight, and more modern physiology, and they could escape from predators more easily and could get access to more food resources."
