Protelytroptera, which are similar to modern Blattodea (cockroaches) with shell-like forewings and the large, unequal anal fan, are known from the Permian of North America, Europe and Australia. No fossils from the Triassic — during which Dermaptera would have evolved from Protelytroptera — have been found. Amongst the most frequently suggested order of insects to be the closest relatives of Dermaptera is Notoptera, theorized by Giles in 1963. However, other arguments have been made by other authors linking them to Phasmatodea, Embioptera, Plecoptera, and Dictyoptera. A 2012 mitochondrial DNA study suggested that this order is the sister to stoneflies of the order Plecoptera. A 2018 phylogenetic analysis found that their closest living relatives were angel insects of the order Zoraptera, with very high support. Archidermaptera is believed to be sister to the remaining earwig groups, the extinct Eodermaptera and the living suborder Neodermaptera (= former suborders Forficulina, Hemimerina, and Arixeniina). The extinct suborders have tarsi with five segments (unlike the three found in Neodermaptera) as well as unsegmented cerci. No fossil Hemimeridae and Arixeniidae are known. Species in Hemimeridae were at one time in their own order, Diploglassata, Dermodermaptera, or Hemimerina. Like most other epizoic species, there is no fossil record, but they are probably no older than late Tertiary. Some evidence of early evolutionary history is the structure of the antennal heart, a separate circulatory organ consisting of two ampullae, or vesicles, that are attached to the frontal cuticle near the bases of the antennae. These features have not been found in other insects. An independent organ exists for each antenna, consisting of an ampulla, attached to the frontal cuticle medial to the antenna base and forming a thin-walled sac with a valved ostium on its ventral side. They pump blood by elastic connective tissue, rather than muscle. Taxonomy Distinguishing characteristics The characteristics which distinguish the order Dermaptera from other insect orders are: General body shape: Elongate; dorso-ventrally flattened. Head: Prognathous. Antennae are segmented. Biting-type mouthparts. Ocelli absent. Compound eyes in most species, reduced or absent in some taxa. Appendages: Two pairs of wings normally present. The forewings are modified into short smooth, veinless tegmina. Hindwings are membranous and semicircular with veins radiating outwards. Abdomen: Cerci are unsegmented and resemble forceps. The ovipositor in females is reduced or absent. The overwhelming majority of earwig species are in the former suborder Forficulina, grouped into nine families of 180 genera, including