A SCOTTISH fossil that has languished in the vaults of London鈥檚 Natural History Museum since the 1920s is the world鈥檚 oldest known insect. Its existence pushes back the origin of winged insects by 80 million years, and could help solve the puzzle of why insects learned to fly.
The fossil creature, Rhyniognatha hirsti, is 400 million years old and comes from near Aberdeen. When Australian entomologist Robin John Tillyard studied it in the 1920s he reported that it might be related to insects, but he couldn鈥檛 be sure. Believing the fossil to be unremarkable, experts since then have largely ignored it.
While gathering photos for a book on insect evolution, entomologist Michael Engel of the University of Kansas in Lawrence and David Grimaldi of the American Museum of Natural History, New York, stumbled on the Rhyniognatha fossil at the London museum and looked at it under a microscope. 鈥淭oday, our microscopes are vastly better than what Tillyard was using,鈥� says Engel. 鈥淎nd when we looked through the scope, we were stunned.鈥�
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They saw that Rhyniognatha had all the hallmarks of a true insect. Far from being a primitive type, it chewed food with efficient scissor-like jaw mouthparts, or mandibles, each with two joints (Nature, vol 427, p 627).
Whether its diet was pollen, leaves or small animals is impossible to say, but its mandible structure is only ever found in winged insects, which is compelling evidence that Rhyniognatha could fly, even though the fossil has no wings. 鈥淭he fossil came from hot springs, and unfortunately, boiling water is not a good place for a wing to be preserved,鈥� says Engel.
Until now, the oldest insect fossils on record were a primitive pair of wingless insects 379 million years old, found in New York state and Canada. Winged insects were thought to have evolved later, some 320 million years ago. But Rhyniognatha suggests insects were flying at least 400 million years ago (see Graphic).
Pushing back the evolutionary origins of insects could help explain why they have become so dazzlingly diverse. 鈥淓ven just the known insect species outnumber all other living things combined,鈥� says Engel. It could also hint at why insects started to fly. Shortly before Rhyniognatha lived, the world鈥檚 plants had sprouted from dwarfs no more than a metre high into giants more than 30 metres tall. It is possible that insects coped with the new environment by learning to glide from treetops to the ground.
Engel hopes to trawl the world鈥檚 famous fossil sites for more insects as old as Rhyniognatha. 鈥淲e would absolutely die to have an entire bug with wings from that period, we could learn so much from their structure.鈥�