Science: How Birds Began to Fly

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Poking through the fossil collection of The Netherlands' Teyler Museum in September, Yale Paleontologist John H. Ostrom spotted one musty specimen that looked odd to his trained eye. It was labeled pterosaur, a flying reptile that inhabited the earth from 65 to 200 million years ago. But when Ostrom held the fossil to the light, he saw the distinctly unreptilian impression of a feather. "My heartbeat began going up fast," recalls Ostrom, who quickly recognized that the specimen was not a pterosaur at all. It was, in fact, a far rarer prehistoric aviator: an Archaeopteryx (literally "ancient wing"), the earliest known bird.

What makes the "newest" Archaeopteryx fossil especially significant is that it may help resolve an old scientific argument about the evolution of birds. According to the more popular theory, birds are descended from small tree-dwelling reptiles that developed crude "wings," like those of the modern flying squirrel. They used those wings for gliding round their arboreal habitats and dodging foes. The other theory says that birds evolved from ground-dwelling reptiles that grew similar membranes, helping them to take increasingly longer leaps after insects and other fast-moving prey.

When he examined the specimen under a microscope, Ostrom noticed a feature on "Archy" that had not been preserved on the three other known Archaeopteryx fossils. It was the faint imprint of a horny sheath—or fingernail-like covering—on the three claws protruding from each of the wings of these ancient birds. Resembling the talons of a contemporary eagle, these razor-sharp, miniature scythes were obviously better suited for catching and slicing up prey than for scampering up the trunks of trees. Thus, Ostrom suggests, Archaeopteryx's lizard-like forebears probably launched themselves into the air from the ground—not from the limbs of ancient trees.