Lead author Dial had expected to observe different wing strokes employed for different behaviors in his study of chukars, quail-like ground birds that live in Eurasia. "They really only need one wing stroke, and they use [their wings] the day they hatch in an aerodynamically meaningfully way—even though they can't fly," Dial said.
(Related news: "Dinosaur-Era Bird Could Fly, Brain Study Says" [August 4, 2004].)
Clues to First Flight?
The way in which vulnerable young birds use their wings while transitioning into adult bodies could be a model for how their ancestors developed the ability to fly, Dial said.
"When you step back and look at the fossils they are finding, the long-legged dinosaurs with half a wing, they look very uncannily like today's birds that are going through the juvenile stage," he said.
"When you look at the development of these animals, you may in fact be looking at the strategies that their ancestors employed to get through transitional states [in evolution]."
(See the evolution of fins to wings.)
Researchers have long debated two theories of flight origin: the arboreal theory, which suggests that tree-dwelling bird ancestors leapt, glided, and eventually flew from branch to branch, and the cursorial theory, which holds that forelimb scales became feathers and eventually lifted running reptiles off the ground.
(Related news: "New Birdlike Dino Adds to Debate on Origins of Flight" [October 18, 2005].)
"This really says that flapping baby wings is more likely the explanation for the evolution of flight," Dial said.
"There is no reason you have to start off talking about ground 'up' or tree 'down.' It's, How did animals deal with the environment that they were in?"
Padian of UC-Berkeley agreed.
"The arboreal-cursorial dichotomy is dead and has been for a long time," he said.
"It's a question of how the flight stroke evolved. You can't fly without a flight stroke. Many things live in trees, and even glide, but never truly fly (flap)."
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