Feathery fossil gives mixed signals about early flight
It's been nearly a century since the Wright Flyer lifted off from the sands of Kitty Hawk. For years many scientists thought that the first birds to fly took to the air the same way—from the ground up, with a running start. But the recent find in China of a primitive dinosaurian relative of birds called Microraptor gui, complete with feathers forming wings on all four of its limbs, seems to blur the picture. Living 120 to 110 million years ago, the crow-size animal looks like it might have flown by gliding from tree to tree.
Many scientists think dromaeosaurs, a group of dinosaurs closely related to today's birds, were living on the ground when they evolved almost all the anatomy needed for flapping their arms. Eventually this arm flapping might have led to a takeoff from a run or a jump.
But the Chinese team that studied M. gui, led by Xu Xing and Zhou Zhonghe of the Institute of Vertebrate Paleontology and Paleoanthropology, doesn't think this animal ran or flapped well enough to take off. Its leg feathers would've tripped it up like a hurdler in a ball gown.
Instead, the ample feathers could have formed an airfoil or parachute similar to those of flying squirrels and other tree-dwelling gliders, the scientists say. Adding in the fact that M. gui came early in the evolution of dromaeosaurs led them to hypothesize that gliding may have played an important role in the initial stages of the development of avian flight. They speculate that gliding from trees gave bird ancestors a chance to practice powered flight, using the forelimb flapping they began to develop on the ground.
Other scientists aren't sure what to make of the new fossil, arguing that gliding doesn't necessarily evolve into powered flight: Why waste energy beating your wings when you could take it easy? And how, they wonder, could M. gui have assumed the spread-eagle posture gliding requires? Dinosaurs normally carried their legs under their bodies; they couldn't move them out to the sides. Some researchers suggest that M. gui's leg feathers weren't useful for flight at all. They might instead have played a role in sexual display, or perhaps to make a tiny dinosaur look bigger. —Christopher P. Sloan
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