Archostemata

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The Archostemata are the smallest suborder of beetles, consisting of 50 living species in five families and over 200 described fossil species.<ref name="Li2023">Template:Cite journal</ref> They are an ancient lineage with a number of primitive characteristics. Antennae may be thread-shaped (filiform) or like a string of beads (moniliform). This suborder also contains the only beetles where both sexes are paedogenic, Micromalthus debilis. Modern archostematan beetles are considered rare, but were more diverse during the Mesozoic.

The term "Archostemata" is used more broadly by some authors to include both modern archostematans as well as stem-group beetles like "protocoleopterans", which some modern archostematans closely resemble to due to their plesiomorphic morphology.<ref name="Boudinot2022">Template:Cite journal</ref> Genetic research suggests that modern archostematans are a monophyletic group. Some genetic studies have recovered archostematans as the sister group of Myxophaga.<ref name="Hörnschemeyer2009">Template:Cite journal</ref>

A 2009 paper argued that the poor diversity of modern Archostemata, compared with the staggering evolutionary success of most other Coleoptera lineages, could be due to the lower efficiency of the thoracic locomotor apparatus, the absence of cryptonephric Malpighian tubules, and competition with other beetles more adapted to angiosperms.<ref name="friedrich2009">Template:Cite journal Template:Erratum</ref>