for National Geographic News
Four wings were better than two for the earliest birds, which became airborne by spreading both their feathered arms and legs, a new study says.
The research suggests that the ancestors of modern-day birds first took to the skies by gliding down from trees.
This study is based on well-known fossils from Germany of Archaeopteryx, the most primitive known bird (related news: "Dinosaur-Era Bird Could Fly, Brain Study Says" [August 2004]).
The fossils were re-examined by paleontologist Nick Longrich from the University of Calgary in Canada, who found that the flying dinosaur's leg feathers have an aerodynamic structure and likely acted as lift-generating "winglets."
Longrich said that his research "puts forward some of the strongest evidence yet that birds descended from arboreal parachuters and gliders, similar to modern flying squirrels."
The study supports the "tree down" theory for the origins of avian flight.
This theory suggests that the immediate ancestors of birds were tree-dwelling dinosaurs that developed the ability to glide and paved the way for self-propelled flight.
The competing "ground up" hypothesis argues that species of terrestrial dinosaurs gave rise to birds by running at high speeds and evolving rudimentary wings that lifted them off the ground.
Fossils of the dino-era bird Archaeopteryx, which lived some 150 million years ago, were first discovered in 1861. Eight further specimens were subsequently unearthed.
While researchers at the time noted feathers on the creature's hind limbs, these were generally thought to be used for insulation or display, not for flying.
Longrich examined the structure and function of Archaeopteryx's hind-limb plumage using the fossil record, including the so-called Berlin specimen.
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