A complete insect from the Late Devonian period

The fossil of a complete insect from the Late Devonian period (approximately 365 million years ago) is presented; it was terrestrial, but its features suggest that modern winged insects had already started to diversify at that early date. A complete Devonian insect fossil The early evolutionary history of the insects is obscure. Fragmentary remains of insect-like arthropods are known from the Silurian to the mid-Devonian periods, 425 million to 385 million years ago, whereas modern insects are known from the Carboniferous period, around 345 million years ago. In between lies a gap, poorly sampled by fossil specimens, during which much evolution is thought to have occurred. Here, André Nel and colleagues present the fossil of a complete insect that sits in that gap, about 365 million years ago in the Late Devonian. The fossil insect was terrestrial, but its features suggest that modern winged insects had already started to diversify at that early date. After terrestrialization, the diversification of arthropods and vertebrates is thought to have occurred in two distinct phases 1 , the first between the Silurian and the Frasnian stages (Late Devonian period) (425–385 million years (Myr) ago), and the second characterized by the emergence of numerous new major taxa, during the Late Carboniferous period (after 345 Myr ago). These two diversification periods bracket the depauperate vertebrate Romer’s gap (360–345 Myr ago) and arthropod gap (385–325 Myr ago) 1 , which could be due to preservational artefact 2 , 3 . Although a recent molecular dating has given an age of 390 Myr for the Holometabola 4 , the record of hexapods during the Early–Middle Devonian (411.5–391 Myr ago, Pragian to Givetian stages) is exceptionally sparse and based on fragmentary remains, which hinders the timing of this diversification. Indeed, although Devonian Archaeognatha are problematic 5 , 6 , the Pragian of Scotland has given some Collembola and the incomplete insect Rhyniognatha , with its diagnostic dicondylic, metapterygotan mandibles 5 , 7 . The oldest, definitively winged insects are from the Serpukhovian stage (latest Early Carboniferous period) 8 . Here we report the first complete Late Devonian insect, which was probably a terrestrial species. Its ‘orthopteroid’ mandibles are of an omnivorous type, clearly not modified for a solely carnivorous diet. This discovery narrows the 45-Myr gap in the fossil record of Hexapoda, and demonstrates further a first Devonian phase of dive