Issue date: 2/12/04 Section: News

A tiny fossil discovered in the 1920s and then largely ignored has been identified as the oldest known insect, scientists report. The discovery pushes back the origins of Earth's most prolific life form some 20 million years.

The new analysis of the 400-million-year-old specimen also suggests that it may have had wings, hinting that winged insects - and insects in general - arose much earlier than had been presumed.

Encased in translucent rock called chert, the fossil is about an eighth of an inch square and reveals a pair of triangular jaws that are strikingly similar to those found only in winged insects, said David A. Grimaldi, curator of entomology at the American Museum of Natural History in New York.

Grimaldi and Michael S. Engel of the University of Kansas report their findings in Thursday's issue of the journal Nature.

Grimaldi said the insect, represented in the fossil by parts of its head and body, was likely about a quarter of an inch long and may have looked like a tiny mayfly. If it had wings, he said, it may have sailed between the knee-high tropical plants of its time, possibly feeding on spores.

Other scientists agree that the fossil - of Rhyniognatha hirsti - is the oldest evidence of insects found to date.

Bill Shear, a professor of biology at Hampden-Sydney College in Virginia, said the new analysis provides ''very strong evidence'' that the jaws are those of an insect and that it may have had wings. The oldest known fossils of winged insects are about 320 million years old.

''We had no idea that insects might have developed wings so early on in their evolutionary history. Either insects have been around for a lot longer prior to this time or wings and flight developed very rapidly after the origin of insects,'' he said.

DNA evidence suggests insects originated about 434 million years ago. Shear said the newly understood fossil pushes the insect fossil record back 20 million years. He said 379-million-year-old insect fragments he found two decades ago in upstate New York had been regarded as the oldest unquestionable insect fossils.

A fossil of a primitive insect found in Canada and described in 1988 was dated at about 390 million years, but some scientists now believe it is a younger fossil that got mixed in far older material.

In any case, Grimaldi said his latest fossil is between about 396 million and 407 million years old. It formed when an insect became encased in crystals that formed around a hot spring like those in Yellowstone National Park.

The fossil was found in Scotland in the 1920s and was described by an Australian scientist in a 1928 paper as possibly an insect, but he was unable to draw a definitive conclusion.

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