Winged insects appear surprisingly ancient.

New analyses of a fossil ignored for decades in a British museum suggest that winged insects may have emerged as early as 400 million years ago, tens of millions of years before scientists expected.

The fossil had been excavated near Rhynie, Scotland, and was first described in the late 1920s. While specimens from related species that were preserved intact at the same site have attracted more scientific notice, this microscopic remnant of an ancient insect's head received only a cursory examination and a name--Rhyniognatha hirsti--before it fell into obscurity.

Rhyniognatha's chewing mouthparts, or mandibles, are robust and triangular, and they sport toothlike projections, says David A. Grimaldi of the American Museum of Natural History in New York. He and his colleague Michael S. Engel of the University of Kansas in Lawrence describe the fossil in the Feb. 12 Nature.

Each 0.1-millimeter-long mandible was attached to the creature's head at two hinge points rather than one. This feature, which increases an insect's chewing power, is found today only in silverfish among insects that have no wings and in many winged insects, including dragonflies.

Unfortunately, the Rhyniognatha specimen doesn't include the body segment to which the wings would have been attached. That part of the insect either wasn't preserved or was lost when the specimen was first prepared for analysis long ago.

A diverse assemblage of winged insects appears suddenly in the fossil record about 330 million years ago, and there are few clues about their evolutionary lineage. Relying mostly on the correspondence of the ancient insect's double-hinged mandibles of modern winged insects, and Grimaldi contend that Rhyniognatha pushes back the presence of winged insects to at least 400 million years ago. That would place their more-primitive progenitors even farther in the past.

If Rhyniognatha had wings, the evolutionary origin of those features probably occurred at least 20 million years earlier, says Conrad C. Labandeira of the Smithsonian Institution in Washington, D.C.

Although the fossil's mouthparts seem to indicate that Rhyniognatha was a member of the group that also contains modern winged insects, there's not much else that's certain, cautions James H. Marden, a biologist at Pennsylvania State University in State College. Rhyniognatha could have been either a terrestrial or an aquatic creature, he notes. It's not even clear whether the fossil is of an adult creature or a larval nymph. In some species, these have double-hinged mandibles.