Much-debated rear wings could have given Microraptor extra help in airborne maneuvers

By Susan Milius

Web edition: October 22, 2012
Print edition: December 1, 2012; Vol.182 #11 (p. 14)

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GREAT CORNERS

Four-winged dinosaurs didn’t have to splay out all their limbs to benefit from the rear pair, instead using the hind legs to maneuver in tight turns.

Credit: 3-D reconstruction by David Krentz

RALEIGH, N.C. — A rethink of four-winged dinosaurs suggests that the much-debated hind wings stayed tucked under the body until deployed in the air for tight turns to dodge branches or chase prey.

Just what a dinosaur did with well-developed feathers on all four of its limbs has been a puzzle since the 2003 unveiling of roughly 130-million-year-old Microraptor gui fossils from northeastern China. The first reconstruction showed the small dinosaur gliding in the air with all four limbs extended outward. A later proposal lowered the hind-limb feathers for a Wright-Brothers biplane of wings. Both arrangements have drawn criticism.

In a simpler solution, the dinosaur could have kept its hind limbs under its body much of the time until needed for banking in a turn, Justin Hall of the University of Southern California said on October 20 at the annual meeting of the Society of Vertebrate Paleontology. Extending a feathery right leg a bit while veering left, or vice versa, could easily have shrunk the turning radius by a notable amount depending on the leg angle, he and his colleagues calculated.

That boost for agility makes more sense aerodynamically than keeping both Microraptor hind limbs extended, Hall said. The probable shape of the hind legs’ feather array wouldn’t have generated much lift, so the extra surface would have been worse than useless for straight-ahead moves. “For every surface, you pay a little drag tax,” said coauthor Michael Habib, also at USC.

In contrast, deft maneuvering would have helped the forest-dwelling M. gui cope with complex obstacles. Also, Habib said, the four-winged dinosaur still had the basic body shape of its terrestrial lineage, and feathered legs and a large tail fan could have helped compensate when in the air.

M. gui may be the best known of four-winged dinosaurs, but paleontologists have since found several more. The researchers’ method of calculating an agility boost should work for all four-winged species, said coauthor Luis Chiappe of the Natural History Museum of Los Angeles County. And, Habib said, agility should matter regardless of whether a four-winged dinosaur could power along in sustained flight or just glide.

Powered flight and gliding downward have developed in quite different evolutionary branches, said Kevin Padian of the University of California, Berkeley. Maneuverability is certainly important to both, but he does not see gliding as an evolutionary baby step on a path toward powered flight.