Megasecoptera in the sense used by Carpenter (1992) are possibly paraphyletic, with the Eubleptoptera being more primitive. The order is difficult to define as distinct from the Palaeodictyoptera when the Eubleptoptera is included, and Carpenter (1992) suggested that Megasecoptera might be merged with Palaeodictyoptera. Such a decision, however, would only further cloud relationships within this lineage, and we have, conservatively, retained the principal lineages pending phylogenetic study. Overall, megasecopterans were relatively smaller than individuals of Palaeodictyoptera. Unlike palaeodictyopterans, an archedictyon was only rarely

6.22. Pseudohymen (Megasecoptera) from the Early Permian of Tshekarda in the Ural Mountains of central Russia. PIN 1700/4153.
6.23. Reconstruction of Mischoptera nigra (Megasecoptera) from the Late Carboniferous of Commentry, France.

present and occurred only in what appear to have been the most primitive families. Megasecoptera had distinct but variable numbers and arrangements of crossveins. Veins Sc and R were positioned close together, and indeed in subgroups of the Megasecoptera there was costalization of the wing margin. Overall, the wings of Megasecoptera could be quite spectacular (Figure 6.22). Like the Palaeodictyoptera, some were patterned, but the patterns were never as bold as those in palaeodictyopterans. However, the petiolate wings were distinctive and probably reflect a unique flight among Paleozoic insects, possibly even hovering (Wootton and Kukalova-Peck, 2000). In addition to the petiolate base, some taxa had distinctly falcate wings and a pronotum studded with spines, making them appear almost fanciful (e.g., Mischoptera) (Figure 6.23). The Megasecoptera have been divided into two groups: those families with distinct paranotal lobes (Eublep-toptera) and those lacking the lobes (Eumegasecoptera and Protohymenoptera), though this is probably an unnatural grouping.

Nymphs are known only of the Mischopteridae and Brodi-idae, which had wing pads that protruded from the body and with a remarkably well-developed venation (Carpenter and Richardson, 1968). Unlike the wing pads of modern insects, the wing pads of Megasecoptera were apparently only joined to the thorax at the point of articulation and were held free at the sides of the body like adult wings. As is generally true for the Palaeodictyopterida as a whole, nymphs lacked gills or any other modifications indicative of an aquatic lifestyle.

The Eubleptoptera (a.k.a., Eubleptidodea) were primitive megasecopterans primitively retaining paranotal lobes, three anal veins, a normal costal space, and numerous crossveins in the wings (frequently with an archedictyon), all features reminiscent of Palaeodictyoptera, which is where Carpenter (1992) had placed them. However, there were distinctly fewer crossveins compared to all other Palaeodictyoptera, similar to that of other Megasecoptera. Eubleptoid families (e.g., Eubleptidae, Namurodiaphidae, Anchineuridae, Engis-opteridae, Sphecocorydaloididae, and "Xenopteridae") are recorded from the Pennsylvanian of Europe (Carpenter, 1963a; Kukalova-Peck and Brauckmann, 1990), North America (Handlirsch, 1906a), and Argentina (Pinto, 1986, 1994) through the Early Permian of Oboro (Kukalova-Peck, 1975). The group is perhaps a stem group to all other Megasecoptera.

The remaining two lineages of Megasecoptera (Eumegasecoptera and Protohymenoptera) are united by the loss of paranotal lobes and the elongate wings (petiolate in many taxa); possession of a single, pectinate anal vein; costalization of the wing (crowding of veins C, Sc, and R); and further reduction in the number of crossveins. The two groups differed principally in extent of the costal space in the crowded anterior wing margin. While the Eumegasecoptera retained a distinct costal space (e.g., Mischopteridae, Corydaloididae, Sphecopteridae, Vorkutiidae, Carbonopteridae, Moravohy-menidae), the Protohymenoptera almost entirely lacked a costal space (e.g., Ancopteridae, Aspidothoracidae, Aspido-hymenidae, Bardohymenidae, Brodiidae, Brodiopteridae, Caulopteridae, Hanidae, Protohymenidae, Scytohymenidae). Both lineages are known from the Pennsylvanian and Permian of Europe and North America, although Protohy-menoptera is also known from the Late Permian of South Africa.

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