"It is a very strange mix of characteristics that are otherwise only known for the unrelated insect groups," said one of the researchers to discover this new group of insects, Günter Bechly, a paleontologist at the State Museum of Natural History in Stuttgart, Germany.
From two adult and about 30 larval fossils that came from the Brazilian fossil deposit and are now contained in collections around the world, the researchers created a new order — a broad category that can contain many species — called Coxoplectoptera. This newly named group of insects is long gone; it has no modern descendants, and the fossils date back 120 million years to the early Cretaceous Period.
Bechly and fellow discoverer Arnold Staniczek, an entomologist at the museum, realized they had found something special when they came across one of the fossilized adult insects already in the museum's collection while working on a book on the Crato fossil deposit in Brazil from which it came.
This deposit has produced tens of thousands of well-preserved fossils during a crucial period for insect evolution, according to Bechly.
Each larva had a body shape that is taller than wide, resembling that of a freshwater shrimp. Based on the larva's shortened mid and hind legs, its thick exoskeleton, beak, large antennae and preying-mantis-like forelimbs, these young insects most likely burrowed part way into the mud underwater and waited to ambush smaller insect prey as they passed, the researchers speculate.
Although it shares characteristics with a number of other insects, Coxoplectoptera's closest living relatives are mayflies. These modern, ephemeral insects die after a brief adult life, of two to three hours to two to three days at most, meant only for reproduction. As adults, they do not eat, said Staniczek. Their ancient relative, however, appears to have been more robust, and like juvenile mayflies, carnivorous.
Coxoplectopterahad forelegs designed for catching and gripping, as well as mouthparts capable of eating — something modern mayflies do not have, he said.
These new insects' anatomy may offer a clue to solving a debate about the origin of insects' wings: Did they start out as stiff outgrowths from plates on the back of the thorax, or midsection, or are insect wings derived from mobile, leg-like appendages? The researchers found evidence in Coxoplectoptera that the wings originated in the back plates; however, these proto-wings appear to have incorporated genes from legs.
The research, with assistance from Roman Godunko, of the University of South Bohemia in the Czech Republic and the State Museum of Natural History in Ukraine, appears in a special issue of the journal Insect Systematics & Evolution.