Why some ancient birds had four wings

Modern birds — especially species with big, majestic wingspans — are studies in aerodynamic efficiency, slicing through the air in ways our finest aircraft can't. But it wasn't always that way. Paleontologists in China have discovered that some long-forgotten ancestors of birds were endowed with a much more inefficient set-up: Four feathered limbs designed for flight.

By studying 11 fossils from the lower Cretaceous period 120 million years ago, scientists found clear evidence of hind wings on a few select species. "Modern birds generally work with two wings," says Amina Khan at the Los Angeles Times, "using small, clawed hind legs for ground travel."

According to the Chinese paleontologists, whose findings were published Thursday in the journal Science, the four-legged set-up "may have played an important role in the evolution of flight." These early bird ancestors — species like Microraptor and Sinornithosaurs — were probably in the midst of learning how to use their hind limbs on the ground. Over time, these back wings might have evolved into more functional legs, thus allowing modern hawks to snatch up prey or robins to hunt for worms in the grass.

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Lead researcher Zheng Xiaoting of the Shandong Tianyu Museum of Nature wrote that the hind wings were "aerodynamic in function, providing lift, creating drag and/or enhancing maneuverability, and thus played a role in flight." The debate now, is exactly how these hind wings would have functioned.

In any case, this much is clear: These ancient, multi-winged creatures were probably more terrifying that we ever could have imagined.