Evolution

Did early birds fly with four wings?

It's widely accepted that today's birds evolved from small feathered dinosaurs. The fossils of birdlike dinosaurs have revealed that some had feathers not only on their arms, but on their legs as well. However there was little evidence of early birds sharing these feathers, and it was unknown whether they had already abandoned them before taking to the skies.

But 11 early bird fossils, collected from Liaoning in China, clearly show feather imprints. These fossils date back to the Cretaceous Period and belong to several groups, indicating that this was closer to a trend than a rarity.

But these fossils have only told us that leg feathers were present - they are silent on their function. The paper's authors believe they were used for flight, helping the bird to turn and providing lift. However other scientists disagree, pointing out that proper tests haven't yet been conducted and noting these feathers would have created drag. Some have suggested they may have just been for courtship. Until more fossils are found and more studies conducted, we won't know which hypothesis best explains hindlimb feather function.

Photo credit: Science/AAAS.

Further reading and sources:
http://phenomena.nationalgeographic.com/2013/03/14/the-rise-and-fall-of-four-winged-birds/

http://www.livescience.com/27898-early-birds-sported-4-wings.html

http://www.nature.com/news/early-birds-flew-on-four-wings-1.12613

http://phys.org/news/2013-03-early-birds-wings.html