Why Fly? Flightless Bird Mystery Solved, Say Evolutionary Scientists
Ostriches, emus, moas, and other flightless birds of the world evolved flightlessness separately.
by Allison Fromme
Large flightless birds are scattered across all but one of the world’s southern continents. Since Darwin’s era, people have wondered: How are they related?
Ostriches, emus, cassowaries, rheas, and kiwis can’t fly. Unlike most birds, their flat breastbones lack the keel that anchors the strong pectoral muscles required for flight. Their puny wings can’t possibly lift their heavy bodies off the ground. These flightless birds, called ratites, are clearly different from other avian species.
Darwin noticed, and he predicted that ratites were related to each other. His contemporary, Thomas Huxley, found another commonality among them: The arrangement of bones in the roofs of their mouths appeared more reptile-like than that of other birds.
At about the same time, another biologist, Richard Owen, assembled the remains of a giant ostrich-like fossil skeleton, the first extinct moa known to the western world. But a pesky detail puzzled Huxley: Small, ground-dwelling South American tinamous didn’t seem to fit neatly with the ratites or other birds…
(read more: National Geo)
photo: Christian Ziegler, National Geo