Fossil find supports 'four-winged birds' theory

A theory that birds may have had four wings during a stage of their evolution has been given fresh support with the discovery of a new fossil in China.

The so-far unnamed creature, which lived between 124-million and 145-million years ago, belonged to an extinct group of primitive flying birds called the enantiornithines.

Scientists have found signs of long curved feathers on its legs that suggested a “residual aerodynamic function”, it was reported in the journal Nature.

The tail feathers were short compared with those of modern birds, but it is thought the birds could have gone through a “four-winged” phase in evolution before the tail developed its current aerodynamic shape.

Tail feathers of modern birds contribute to lift during flight.

But some modern birds rely on their legs for assistance when flying. For example, the kittiwake spreads out its webbed feet to act as an air brake, while the lappet-faced vulture stretches its legs and feet to achieve a steep dive onto a kill. The razorbill also flies with the help of its feet.

The new fossil is reminiscent of Microraptor, a squirrel-sized gliding dinosaur known to have had long leg feathers to help it stay aloft.

Evidence recently came to light that Archaeopteryx, the earliest known flying bird, also had feathered legs.

The enantiornithine was discovered in an area of north east China which has yielded numerous fossil birds and feathered dinosaurs.

Reporting on the find, Fucheng Zhang and Zhonghe Zhou from the Chinese Academy of Sciences in Beijing, wrote: “The weak aerodynamic features of the leg feathers of the new bird could have helped the poorly developed tail in manoeuvring during flight, rather as the modern razorbill uses its large webbed feet to supplement its small tail during slow flight.

“The leg feathers of Archaeopteryx and the new enantiornithine fossil may represent vestigial examples of a feature that made an important contribution to flight in early birds.” - Sapa-DPA

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