As any ostrich knows, getting off the ground requires more than just wings and feathers. A thorough study of the earliest known bird, Archaeopteryx, provides evidence of the specific neural machinery thought to be necessary for flight.

Living in the late Jurassic period, Archaeopteryx had the feathered wings and wishbone of a bird but the teeth and long bony tail of a reptile. When paleontologists discovered the first fossil in 1861, some touted it as verification of the then recently proposed theory of evolution. "It was a transitional form," comments Timothy B. Rowe of the University of Texas at Austin, "exactly as Darwinians would have predicted." The origin of birds was one of the biggest battlegrounds of the early discussions on evolution, and part of that debate centered on whether Archaeopteryx could fly.

Previous research focused on aerodynamics and feather shapes, but Rowe and his colleagues searched for avian features in the skull of the first Archaeopteryx skeleton, which is 147 million years old. They took 1,300 x-ray images of the inch-long head to create a 3-D reconstruction of the brain case with computed tomography (CT). The results, published today in Nature, show that the volume of this primitive bird's brain was 1.6 milliliters, which is smaller than that of modern birds of the same size, but larger than that of reptiles. The enlarged visual center and inner-ear canals of Archaeopteryx, however, are very similar to those of flying birds. The authors contend that the great vision and balance skills implied by these brain structures are necessary attributes for flight.

According to Lawrence M. Witmer of Ohio University, conventional wisdom holds that "Archaeopteryx could go airborne but was probably not a very good flier." In an accompanying commentary, Witmer notes the similarities between these new CT scans and those of reptiles known as pterosaurs, which started flying almost 100 million years before the first bird arrived on the scene. "We used to think that feathers made the bird," Rowe remarks, but the skulls of these ancient aviators suggest that "you have to put in a big computer to fly." --Michael Schirber

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