The earliest flying birds had upper and lower wings resembling the biplane design used by the Wright brothers, researchers have claimed.
Scientists reconstructing the fossilised remains of a microraptor gui have concluded that its legs were aerodynamically feathered and acted as a second set of wings to help it glide between trees.
Previous analysis of the four-winged bird raised serious doubts about its ability to fly. The latest study pinpoints a biplane wing arrangement rather than the previously suggested positioning of one pair behind the other. A biplane configuration, the US researchers argue, allowed it to glide, whereas having wings front and back would have created turbulence.
They said: "Aircraft designers have mimicked many of nature's flight inventions. Now it seems likely that the microraptor invented the biplane 125 million years before the Wright 1903 Flyer."
The bird is estimated to have weighed 1kg, had a maximum wingspan of 94cm and could have glided further than 40m. Microraptor is related to archaeopteryx, thought to be the first bird to have discovered flight by flapping its wings, informs The Australian.
Researchers originally suggested that Microraptor spread both arms and legs to the sides of its body to form two pairs of gliding wings. But palaeontologist Sankar Chatterjee of Texas Tech University in Lubbock, US, says that would have been aerodynamically inefficient and that Microraptor's legs could not be splayed sideways.
He says the dinosaur instead folded its legs under its body like modern raptors catching prey, with its long leg feathers sticking out to the side. The asymmetric foot feathers must have had their narrow side facing forward to smooth the flow of air around the leg.
"Once you do this, you have no other choice but the biplane design," Chatterjee told New Scientist. This creates a second set of wings below the body and behind the arm wings, which is "a more anatomically and aerodynamically stable configuration", he believes.