Anchiornis huxley, a small, feathered, dinosaur, showing a second set of wings on its legs. Photo: Dailymail

Researchers have uncovered new evidence that the first birds had four wings instead of two.
A team from China say they flew rather like a biplane -- with wings on their legs providing a second boost.
The team analysed 11 bird skeletons from between 150 and 100 million years ago, and believe they eventually shed the second set so they could use their legs more effectively.
Led by Xiaoting Zheng of China's Linyi University, the authors of the new study analysed the bird skeletons donated by various collectors to the Shandong Tianyu Museum of Nature.
The 11 birds come from five species and were relatively robust: larger than a crow but smaller than a turkey.
Recently, several fossils have shown that some dinosaurs had large feathers on both fore limbs and hind limbs.
But, until now, no examples of this four-winged body plan have been described in birds -- or even in their most recently extinct relatives.
Zheng and colleagues studied fossils in China's Shandong Tianyu Museum of Nature and identified 11 primitive bird species with clear signs of feathered hind legs.
Modern birds have two types of feathers: vaned feathers that cover the outside of the body, and the down feathers that grow underneath them.
The Chinese team found that one type of vaned plumage, also known as pennaceous feathers, was neatly preserved in skeletal fossils of these specimens, along each creatures' hind limbs.
These findings suggest that this four-winged condition preceded the two-winged body plan, and that birds have gradually lost the feathers on their hind limbs over evolutionary time.
In a related news article also published in Science, Michael Balter compares the ancient birds to biplanes in the early 1900s, which were later phased out in favour of faster monoplanes.
The study adds to existing theories that suggest the first birds flew with four wings.