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 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, say the insect probably had 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 jaw 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.
Other researchers say the question is unresolved, but agree that the creature's true identity represents a major find in a field with a scarcity of early insect fossils.
Grimaldi said the finding means that insects likely originated by the Silurian period, at least 425 million years ago. Scientists have seen the earliest evidence of a plant invasion from water during this period - a coincidence not lost on most researchers.
Many believe there was an intimate association between insects and plants as they appeared on land - that the former fed on spores at the tips of the latter's branches. One hypothesis suggests that wings developed to enable insects to make the most of that relationship.
The implication that insects existed earlier than previously believed means they may have had ample time to evolve in the relative absence of other terrestrial life. The addition of wings could have led to even greater success, especially at a time when the sky was an open niche for the earliest terrestrial creatures.
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