A 400 million-year-old creature no larger than a grain of rice has laid claim to the title of world’s oldest insect, according to a study published today in the journal Nature.

The new identification, researchers say, pushes the presumed origins of insect life back by tens of millions of years and sheds new light on the question of why insects now dominate much of the Earth, both in terms of diversity and ecological impact.

The creature’s partial remains, fossilized within a layer of rock and unearthed about 80 years ago in Rhynie, Scotland, lay largely forgotten within London’s Natural History Museum until two American entomologists recently re-examined the fossil under a microscope. They found that the animal, known as Rhyniognatha hirsti and dated to between 396 million and 407 million years old, possessed the well-developed mandibles of a true insect rather than of a more primitive precursor.

University of Kansas entomologist Michael Engel and study co-author David Grimaldi, a curator of invertebrate zoology at the American Museum of Natural History in Manhattan, also argue that the insect likely boasted the earliest known set of wings.

The fragmentary nature of the newly identified creature, whose fossilized remains include little more than its head, leaves open the question of whether the insect had wings, but Grimaldi said its mandible structure strongly suggests that it did.

Grimaldi said the fossilized triangular-shaped mandibles revealed two joints and a broad incisor region and molar region — the same basic structure seen in most winged insects and one more evolutionarily advanced than that of modern mayflies, considered more primitive than other winged insects today.

"The fact that it has mandibles that are even more highly evolved than mayflies really does strongly suggest that this thing was a winged insect," he said.

Grimaldi said the finding means that insects likely originated by the Silurian period, at least 425 million years ago.