Pterygota group comprises 99.9% of all insects.[4] The orders not included are the Archaeognatha (jumping bristletails) and the Zygentoma (silverfishes and firebrats), two primitively wingless insect orders. Unlike Archaeognatha and Zygentoma, the pterygotes do not have styli or vesicles on their abdomen (also absent in some zygentomans), and with the exception of the majority of mayflies, are also missing the median terminal filament which is present in the ancestrally wingless insects.[5][6][7]
The oldest known representatives of the group appeared during the mid-Carboniferous, around 328–324 million years ago, and the group subsequently underwent rapid diversification. Claims that they originated substantially earlier during the Silurian or Devonian based on molecular clock estimates are unlikely based on the fossil record, and are likely analytical artefacts.[8]
Systematics
This section needs to be updated. The reason given is: Highly outdated; for example, "Exopterygota" is almost certainly considered paraphyletic by most phylogenetic studies in the last 10 years at least by now, as most of them instead recognise at least Polyneoptera and sometimes Paraneoptera (e.g. [9]), with the Paraneoptera more closely related to Holometabola than Polyneoptera.. Please help update this article to reflect recent events or newly available information. Last update: August 2007(December 2023)
Traditionally, this group was divided into the infraclassesPaleoptera and Neoptera.[10] The former are nowadays strongly suspected of being paraphyletic, and better treatments (such as dividing or dissolving the group) are presently being discussed[citation needed]. In addition, it is not clear how exactly the neopterans are related among each other. The Exopterygota might be a similar assemblage of rather ancient hemimetabolous insects among the Neoptera like the Palaeoptera are among insects as a whole. The holometabolousEndopterygota seem to be very close relatives, indeed, but nonetheless appear to contain several clades of related orders, the status of which is not agreed upon.
The following scheme uses finer divisions than the one above, which is not well-suited to correctly accommodating the fossil groups.
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