Paleopterous and neopterous insects
Two groups of pterygotes evolved the ability to fold their wings back flat against their abdomens. The largest of these is the clade Neoptera ("new wing"). Remaining insects (all of the taxa in the above tree except for Neoptera) are sometimes referred to as Paleoptera ("old wing"), because they lack the sophisticated wing-folding mechanism of neopterous insects. Members of paleopterous insects cannot fold their wings back over their abdomens, with the exception of the extinct order Diaphonopterodea, which could fold their wings using a mechanism different than Neoptera. (Some neopterous insects, such as butterflies, can no longer fold their wings against their abdomen, but this clearly represents a secondary loss.)
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