Nearly every insect you meet descends from the winged experiment
Pterygota—“winged”—is the insect subclass holding all winged insects and lineages that secondarily lost wings, about 99.9% of insect species. Only jumping bristletails and silverfish/firebrats stay outside as primitively wingless. Mid-Carboniferous fossils around 328–324 million years ago already show the group diversifying fast.
The subclass takes its name from a Greek word meaning winged, and it embraces every insect that flies plus the lineages that later gave up their wings. That adds up to 99.9 percent of all insect species. Only two orders stand outside it: the jumping bristletails, Archaeognatha, and the silverfish and firebrats, Zygentoma, both wingless from the start rather than by loss.
Anatomy separates the two camps even where wings are missing. Pterygotes lack the small styli and vesicles found on the abdomen of the primitively wingless orders, though some zygentomans lack them too. Apart from most mayflies, they have also lost the central tail filament that the ancestral wingless insects still carry.
The earliest fossils date to the middle of the Carboniferous, roughly 328 to 324 million years ago, after which the group diversified quickly. Some molecular clock studies place its origin much earlier, in the Silurian or Devonian, but the fossil record argues against this, and those dates are probably artefacts of the analysis.
How the branches fit together is still argued over. The classic division into two infraclasses, Paleoptera and Neoptera, is in doubt because Paleoptera probably does not form a single natural group, and researchers are debating whether to split or abolish it. Within Neoptera, the Exopterygota, ancient insects that develop through gradual metamorphosis, may be a similarly loose assemblage, while the Endopterygota, which undergo complete metamorphosis, look closely related yet contain several disputed clusters of orders. Finer schemes accommodate fossils better, listing extinct orders such as Permothemistida, Meganisoptera and Protozygoptera beside living ones: dragonflies and damselflies (Odonata), cockroaches and termites (Blattodea), booklice, barklice and lice (Psocodea), and the twisted-winged parasites of Strepsiptera.
Source: Pterygota
