THE ORIGIN AND EVOLUTION OF HYMENOPTEROUS INSECTS [p. 24] Chapter 3 EVOLUTION OF THE INFRACLASS SCARABAEONES A. P. Rasnitzyn* Dragonflies [order Odonata] and mayflies [order Ephemeroptera], which have retained a primitive thorax structure (absence of a cryptosternum) but are specialized in other respects, occupy the most isolated position in the infraclass. They are similar to each other in a number of characters, but the nature of the latter does not allow drawing a conclusion about any close relationship of the two orders. Indeed, the primitiveness of the structure of the thorax common to both of them, like any symplesiomorphy, is not evidence of a common origin. The adaptations of the larvae of mayflies and dragonflies to an aquatic way of life are different, and they show, rather, an independent transition to development in water. The loss of the ability to fold the wings as well is connected with different processes in them: in mayflies, with the ephemerality of the imago, the function of which is essentially limited to nuptial flight and oviposition; and in dragonflies, with the metamorphosis of the adult insect to an active aerial predator. It is highly probable that mayflies and dragonflies are independent evolutionary branches. The belonging of dragonflies and mayflies to a common trunk of Scarabaeones, that is, the isolation of them from Protoptera as part of a single trunk with the remaining members of the infraclass (except Protoptera), is confirmed by the metamorphosis of the style of the ninth segment in mayfly males into part of the copulatory organ [endophallus], and in dragonfly females into a sheath of the ovipositor. The ovipositor in mayflies is reduced; it is unknown what function the styles in females of their ancestors performed, but the very fact of the coincidence of their reduction with the reduction of the ovipositor is indirect evidence of the advantage of the transition of styles as part of the ovipositor, that is, of the similarity of mayflies to dragonflies and higher Scarabaeones as * Original citation: Rasnitsyn, A. P. 1980. Proiskhozhdenie I evoliutsiia pereponchatokrylykh nasekomykh. Trudy Paleontologicheskogo Instituta, Akademiia Nauk SSSR (Transactions of the Paleontological Institute, Academy of Sciences of the USSR) 174:24–35. Translated by Rosanne D’Aprile Johnson; scanned and edited by Abree Murch and Matthew Carrano, Smithsonian Institution, 2014. Brackets [] indicate comments added by original translator. well, according to this character. In an analogous way, the reduction of the primary copulatory organ of dragonflies does not allow judging its initial structure. However, the approximated laying of the anlagen (Makhotin, 1934), typical of most Scarabaeones (except mayflies) and correlating with the distinguishing of the isolated, variably mobile genital capsule in them, points to a similarity of dragonflies (even deeper than in mayflies) to higher Scarabaeones. This allows proposing that dragonflies were separated from the common trunk of the infraclass even later than mayflies. Additional evidence of the same is the later appearance of ocelli [simple eyes] in dragonfly ontogeny, as in Paraneoptera and Oligoneoptera, but unlike bristle-tails, mayflies and Polyneoptera, in which the ocelli already appear at the first postembryonic stage (see Fig. 3). Both dragonflies and mayflies deserve being distinguished into special cohorts, corresponding to Libelluliformes and Ephemeriformes. As has been mentioned, the former are known from the late Namurian and are the most ancient of the now-surviving orders of insects. In spite of their presumably earlier isolation, mayflies really appear only in the Late Carboniferous. This fact does not compulsorily point to the incompleteness of the geological record: it is quite possible that, for example, the ancestors of mayflies only acquired characters typical of the order toward this time. Insects with complete metamorphosis, the cohort Scarabaeiformes (= Oligoneoptera), form a restricted group within Scarabaeones. A sharp differentiation of ontogeny at the stages of primary morphogenesis (egg and chrysalis), feeding and growth (larva), and reproduction and settling down (imago) (Rasnitsyn, 1965a), is characteristic above all. At that, the degree of embryonation of ontogeny (adultization of the first postembryonic stages), minimal compared with that among contemporary pterigotes, is observed only in mayflies. Of the morphological characters common for the imagines of all Scarabaeiformes, it is possible to indicate perhaps only the appearance of the third medial articulation of the middle and posterior coxae with the thorax. The composition and structure of the cohort is discussed later. Two large groups, Paraneoptera and Protorrhynchota, are distinguished among the remaining Scarabaeones. The first, including Psocopteroidea, [p. 25] Thysanopteroidea, and Homopteroidea1, was distinguished by Martynov (1925) as one of three subsections 1 Zoraptera are often attributed to Paraneoptera; however, even the most important characters of similarity of Neopter. The cohort Protorrhynchota was established by B. B. Rohdendorf (1968) for Paleozoic orders of Palaeoptera that were grouped around Palaeodictyoptera. Besides this order, it includes Megasecoptera, Archodonata, and Diaphanopterodea as well, and was contrasted by Rohdendorf with cohort Hydropalaeoptera (Ephemeroptera + Odonata). The basis for distinguishing Protorrhynchota is the structure of their mouth parts, transformed into a pricking-suctorial proboscis. Rohdendorf believed the proboscis structure of Protorrhynchota and Homopteroidea to be identical, and proposed that protorrhynchots were direct ancestors of Homopteroidea, and with them of all paraneopters as well. Objections were advanced against Rohdendorf’s hypothesis (Sharov, 1973), based on existing differences in proboscis structure (in Homopteroidea, the stylets are protected by a sheath from the labium; in Thysanopteroidea, from the labrum; in Protorrhynchota, they are protected only by maxillary palps, and, at least in Diaphanopterodea, by labial palps as well), and on the absence of a proboscis in book lice [order Psocoptera]. The direct descent of all paraneopters from protorrhynchots is really scarcely possible. The opposite hypothesis, of the origin of protorrhynchots from rhynchots, is unacceptable as well, because the most primitive representatives of the latter (Archescytinidae) already possess a specialized proboscis, and in addition appear much later than protorrhynchots (in the Permian). Nevertheless, the phylogenetic connection between protorrhynchots and paraneopters is highly probable, supported by many structural features of the order Hypoperlida. The Hypoperlida forms a diverse and probably rather extensive group of Paleozoic insects that possess characters of advanced Scarabaeones (thorax with a cryptosternum, primarily roof-shaped wing-flexing, posterior wings without bending the anal lobe, ovipositor with sheaths) and display definite connections with Paraneoptera and Protorrhynchota (the tendency toward lengthening the head and mouth parts, which is realized in the shape, similar in detail to that observed among Permian book lice, and which it is possible to regard as an intermediate stage in the formation of the proboscis of of these insects with Paraneoptera (decreased number of Malpighian tubes, free ganglia of the nerve cord, and segments of the tarsi) (see Kristensen, 1975) are not more reliable than those that unite them with Polyneoptera (first of all, the structure of the lower side of the thorax, and in particular the absence of a cryptosternum). On the other hand, not all characters that distinguish Zoraptera from Paraneoptera in Kristensen’s view (1975), are such (ocelli are developed in the nymph of not only Zoraptera, but also Paraneoptera, for example in the late nymphs of Cicadidae). The question of the position of Zoraptera within the insect system needs additional analysis. protorrhynchots). The central family of the order Hypoperlidae (Rasnitsyn, 1977a) is truly known starting in the Late Carboniferous (Fig. 11), but it reaches a special diversity in the Permian (Figs. 12–16), the described forms far from exhausting the material collected from the group. Hypoperlids were described among Paraplecoptera (Martynov, 1928), but Sharov (1961) noted their sharp distinction from both Paraplecoptera2 and Plecoptera, and indicated the need for a revision of their systematic position. Many members of the family (Dinopsocus Martynov = Martynopsocus Karny, Kaltanelmoa Rohdendorf, Fatianoptera O. Martynova) were described as special families in different orders of insects (Psocoptera, Diaphanopterodea, and Raphidioptera, respectively), but at least for Martynopsocus, its similarity to Hypoperlidae has been mentioned (Sharov, 1961). True finds of hypoperlids outside the U.S.S.R. are not known, but it is quite possible that some Carboniferous insects belong to them, including also the Namurian of Europe and North America, especially Ampeliptera Pruvost (Fig. 17) and Aenigmatodes Handlirsch (Fig. 18). Also other Carboniferous insects, which were partially mentioned above in connection with the order Protoptera, could turn out to be close to hypoperlids: Limburgina [p. 26] 2 Subsequently Protoblattodea (Sharov, 1968). Figs. 11– 16. Representatives of the Family Hypoperlidae. 11 – Tshunicola carbonarius A. Rasn.; Upper Carboniferous of the Tungusskiy Basin; 12 – Hypoperla elegans Mart.; Upper Permian of the Arkhangel’sk