Flying Aces of the Carboniferous

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Gretchen Vogel
1998-10-22 17:30
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To catch prey like mosquitoes and houseflies, dragonflies zoom and hover with extremely efficient, highly responsive wings--a feature many aerospace engineers would like to imitate. But nature had quite a head start. In tomorrow's Science, researchers describe evidence for a shape-changing wing in a 320-million-year-old dragonfly from Argentina.

Birds and bats flex muscles to control the shape of their wings. In contrast, dragonflies rely on a complex network of veins that stabilizes and shapes the wings without any muscle power. That's "smart engineering," says entomologist Robin Wootton of the University of Exeter, United Kingdom. He cites a series of pleats arranged so that when the insect flaps downward, air pressure below the wing forces the trailing edge to stiffen and curve down in a classic airfoil shape. Roughly similar to the flaps that open on planes during takeoff and landing, the mechanism allows dragonflies to stay aloft at lower speeds.

That's not a new trick, apparently. Wootton and paleoentomologist Jarmila Kukalová-Peck of Carleton University in Ottawa noticed a similar design when they examined a well-preserved, 8-centimeter dragonfly fossil from La Rioja, Argentina. When Wootton, an expert on the mechanics of insect wings, built a 3-dimensional paper copy of the wing region, it behaved like the modern dragonfly's.

The specimen shows how quickly insects evolved sophisticated aerodynamics, says insect flight physiologist Robert Dudley of the University of Texas, Austin. Not only did evolution come up with such sophisticated flying adaptations only 10 million years after the first known insect flight, but it also engineered them at least twice, because the fossilized specimen is not a direct ancestor of modern dragonflies. "It's a startling example of convergent evolution," says evolutionary aerodynamicist Adrian Thomas of Oxford University in the U.K.

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