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Palaeoptera (class Insecta, subclass Pterygota) One of the two infraclasses (compare NEOPTERA) into which insects are placed according to the position in which they hold their wings when at rest. Members of the Palaeoptera are unable to fold their wings; when the insect rests its wings are held out as they are when it is flying; this is the more primitive condition. The infraclass includes the mayflies (Ephemeroptera) and dragonflies (Odonata). The distinction between the two infraclasses emerged in the Carboniferous, very early in insect evolution, and is known from fossils of that period.