Evidence for wing development in the Late Palaeozoic Palaeodictyoptera revisited.

The numerous fossil specimens described as consecutive series of different larval stages of two species, Tchirkovaea guttata and Paimbia fenestrata (Palaeodictyoptera: Tchirkovaeidae), were reinvestigated with emphasis on comparing the development and growth of their wings with that of the wings of a recent mayfly, Cloeon dipterum. This unique fossil material was for a long time considered as undisputed evidence for an unusual type of wing development in Palaeozoic insects. The original idea was that the larvae of Palaeodictyopterida had wings, which were articulated and fully movable in their early stages of postembryonic development and that these gradually enlarging wings changed their position from longitudinal to perpendicular to the body axis. Moreover, the development of wings was supposed to include two or more subimaginal instars, implying that the fully winged instars moulted several times during their postembryonic development. The results of the present study revealed that there is no evidence that this series of nymphal, subimaginal and imaginal wings provide support for the original idea of wing development in Palaeozoic insects. On the contrary, our results indicate, that the supposed palaeodictyopteran larval wings are in fact wing pads with a wing developing inside the cuticular sheath as in recent hemimetabolous insects. Moreover, this study newly reinterpreted the wing pad base of Parathesoneura carpenteri and confirmed the presence of nygma like structures on wings and wing pads of palaeodictyopteran Tchirkovaeidae.

Life history, systematics and flight ability of the Early Permian stem-mayflies in the genus Misthodotes Sellards, 1909 (Insecta, Ephemerida, Permoplectoptera).

BACKGROUND: The stem-group of Ephemeroptera is phylogenetically important for understanding key steps in evolutionary history of early pterygote insects. However, these taxa have been mostly studied from the taxonomy point of view focused on the pattern of wing venation and often using only classical optical microscopy devices. In-depth studies on detailed morphology of the different body structures are scarcely performed, although the results are critical for elucidation of life history traits and their evolutionary pattern among the basal pterygotes. RESULTS: New information is presented on the morphology of two species of Misthodotes, which are stem-mayflies from the Early Permian. Based on new results obtained from a re-examination of the type specimens and supplementary material, we infer the life history traits of both the adult and larval stages of these Palaeozoic insects and reconsider previous interpretations. For the first time, we report the structure of the thoracic pleura and the articulation at the base of the wing in a stem-group of Ephemeroptera and compare them with those of extant mayflies. We also provide additional support for the systematic placement of investigated taxa and an amended diagnosis of the genus Misthodotes. CONCLUSIONS: Adult Misthodotes sharovi and Misthodotes zalesskyi had chewing mouthparts, which enabled them to scavenge or feed on plants. The wing apparatus was adapted for slow powered flapping flight and gliding, using long caudal filaments for steering. The wing base does not have rows of articulary sclerites as previously hypothesized for some Palaeozoic taxa but inflexible axilla similar to that found in modern mayflies. The structure of the thoracic pleura is also similar to that in the crown group of Ephemeroptera, while differences in the course of sutures may be explained by an evolutionary trend towards more powerful dorsoventral flying musculature and forewing-based flight (anteromotorism) in modern taxa. There is no evidence for swarming behaviour and mating in the air as occurs in modern mayflies as they had none of the associated morphological adaptations. Putative larvae of Misthodotes can not be unambiguously associated with the adults. They also exhibit some morphological specializations of Protereismatidae like 9 pairs of abdominal tracheal gills supporting their benthic lifestyle with legs adapted to burrowing.

Male postabdomen reveals ancestral traits of Megasecoptera among winged insects.

External male genitalia of insects are greatly diverse in form and frequently used in evolutionary context and taxonomy. Therefore, our proper recognition of homologous structures among various groups from Paleozoic and extant insect taxa is of crucial interest, allowing to understand the key steps in insect evolution. Here, we reveal structural details of two Late Carboniferous representatives of Megasecoptera (families Bardohymenidae and Brodiopteridae), such as the presence of separated coxal plates VIII and ventral expansions of coxal lobes IX. Together with the confirmed presence of abdominal styli in some other members of Palaeodictyopterida (Diaphanopterodea) this suggests that early pterygotes may have had traits more archaic than expected. Whether or not these traits point to a stem-group relationship of Palaeodictyopterida to all other Pterygota as suspected by earlier authors remains unclear at this stage. Furthermore, the present study provides an updated comparison of male postabdomen morphology among extant species of wingless Archaeognatha and representatives of early diverging groups of Pterygota from the Late Carboniferous and Early Permian, the Megasecoptera (Palaeodictyopterida), Permoplectoptera (Ephemeroptera) and Meganisoptera (Odonatoptera).

On the morphology of the Late Paleozoic insect families Bardohymenidae and Aspidothoracidae (Palaeodictyopterida: Megasecoptera).

Megasecoptera is a late Paleozoic order of herbivorous insects with rostrum-like mouthparts and slender homonomous outstretched wings. Our knowledge of their morphology is mainly based on wings while other body parts are scarcely documented. Here we focus on the families Bardohymenidae and Aspidothoracidae. A new well preserved specimen of Sylvohymen cf. sibiricus is described and illustrated, particularly the structures of the external male genitalia previously unknown for Bardohymenidae. Sylvohymen marginatussp. nov. is described from the early Permian of Tshekarda based on unique traits in the wing venation. The genera Paleohymen and Taigahymen are both removed from Bardohymenidae and the latter is transferred to Vorkutiidae. Alexahymen aestatis (Brauckmann, 1991) comb. nov. from Pennsylvanian at Piesberg is transferred from Aspidothoracidae to Bardohymenidae. Piesbergbrodiagen. nov. is designated for Piesbergbrodia tristrata (Brauckmann and Herd, 2003) comb. nov. as a member of Brodiidae and the first known record of this family from Piesberg quarry. The placement of Sylvohymen peckae in the Bardohymenidae is considered doubtful due to lack of significant characters in its venation. Furthermore, our study is focused on the form of the apical cell and the pattern of wing pigmentation. Peculiarities of the integumental outgrowths and external genitalia of representatives of Aspidothoracidae and Bardohymenidae, and other close relatives, are highlighted.

New mayfly genera from the Middle Triassic of Poland and their evolutionary and paleogeographic implications (Ephemerida: Litophlebiidae, Vogesonymphidae).

Two new mayfly genera and species from the Triassic deposits of the Palegi area (southeast Poland) are described. This is the first description of aquatic insects from the Palegi locality. Triassolitophlebia palegica gen. et sp. nov. (Litophlebiidae) is established on the basis of an isolated forewing. This is the first finding of this family in the Northern Hemisphere, known previously only from the Molteno Formation (South Africa). This is also the first mayfly family from the Triassic which has been found in both Hemispheres, providing additional evidence of the presumed similarity of aquatic insect faunas in the Southern and Northern Hemispheres during the Triassic. The consistent wing venation of ancient mayflies with homonomous wings could be evidence that they originated from the same ancestor. The second new mayfly, Palegonympha triassica gen. et sp. nov. (Vogesonymphidae), is described on the basis of a single fossil nymph (imprint of the exuviae) and indicates the similarity of the Palegi arthropod assemblage to that described from the Middle Triassic of France. The presence of a mayfly nymph in the last instar stage suggests not only that the Palegi deposit represents a fluvial environment with well-oxygenated and limpid water but also that these conditions lasted long enough to allow for such development.