By Paul Rincon
BBC News Online science staff
A tiny fossil preserved in red sandstone from Scotland has been identified as the oldest known insect.
Rhyniognatha shares features with winged insects
The fossil suggests insects were among the earliest animals to live on land and that winged flight may have emerged earlier than previously thought.
The fragmentary specimen from Rhynie in Aberdeenshire comes from deposits dated to between 396 and 407 million years old, during the Devonian Period.
Details of the discovery are published in the scientific journal Nature.
The discovery suggests that insects almost certainly evolved in the Silurian Period, some 438-408 million years ago.
"In the late Silurian is where we have the first evidence for terrestrial ecosystems, so it really says that insects were represented in the earliest ecosystems on land," co-author Michael Engel of the University of Kansas, US, told BBC News Online.
Anatomical characteristics of the fossil's jaw identify it as a true insect, Dr Engel and co-author David Grimaldi write in Nature.
Rhyniognatha hirsti shares features with winged insects, suggesting that winged flight emerged much earlier than previously thought.
Rhyniognatha could have had wings, say the authors, but this is impossible to confirm since the wings themselves are missing.
"The first preserved wings come from about 330 million years ago. By that time you have a diversity of winged insects present," said Dr Engel.
"In terms of the origin of flight and the radiation of winged insects, you've already missed the party.
"To have this incredible array of forms they must have been around before."
Dr Engel speculates these early insects might have fed on plant sporophylls - which occur at the tips of branches and bear sporangia, the spore-producing organs.
Insect flight could have evolved in tandem with the dramatic increase in the size of plants during the Devonian. Wings could have helped insects to control their descent from branches to the ground.
The fossil was first described in 1926 by the entomologist Robin John Tillyard. The specimen is now kept at the Natural History Museum in London.
"It has been known for some time and various people have scratched their heads over it," said Dr Lyall Anderson of the National Museums of Scotland in Edinburgh.
The Rhynie cherts were deposited under unusual conditions. Hot springs and geysers fed the area with fluids rich in dissolved silica.
As the hot water cooled, the mineral silica crystallised, entombing the animals and creating a 3D impression of their bodies.
Many deposits of this age are formed when different layers of material press down on each other, squashing fossils contained in them.
Previously, the oldest known insect was a wingless specimen of the species Archaeognatha or Zygentoma, fragments of which are preserved in 379 million-year-old rocks from New York, US.
The findings agree with a DNA study by Michael Gaunt and Michael Miles of the London School of Hygiene and Tropical Medicine in London.
The study estimated that insects emerged about 434 million years ago, in the early Silurian.