The wing venation of the Triassic stem-Odonata Triassoneura andersoni Riek, 1976 (Insecta) brings homologies in the basal complex back to the drawing board

The description of material of the Triassic stem-Odonata Triassoneura andersoni Riek, 1976 (Molteno Formation, South Africa), including the single forewing described to date and hitherto unpublished material, including the well-preserved basal half of a hindwing, led to an in-depth reconsideration of the classical proposal that Anisoptera Selys Longchamps, 1854 (dragonflies), Zygoptera Selys Longchamps, 1854 (damselflies) and Anisozygoptera Handlirsch, 1906 share a homologous discoidal cell (forming the triangle/supratriangle area in Anisoptera, and the quadrangle in Zygoptera). Focusing on the basal complex, composed of the discoidal cell and several surrounding elements, we first compared the Triassic species to the extant anisozygopteran Epiophlebia superstes (Selys Longchamps, 1889). The rare morphology observed in some hindwings of the latter is best explained by a mosaic of fore- and hindwing features, indicating that the first strengthened cross-vein occurring in the MA-MP area cannot be homologous (or, more adequately, homonomous) among the fore- and the hindwing, and neither is the cell it closes proximally. Considering then the Jurassic stem-anisopteran Heterophlebia buckmani (Brodie, 1849), including a rare hindwing morphology similar to that documented in Epiophlebia superstes, further reinforces the previous inferences, but also shows that introgression of morphological features from one wing pair to the other is a rampant phenomenon in Odonata Fabricius, 1793. With this perspective, the morphology of the basal complex in Anisoptera, exemplified by the extant Aeshna cyanea (Müller, 1764), is best explained by the hypothesis that, at some stage along the stem of the group, the hindwing configuration integrally replaced that of the forewing (i.e., that the latter was ‘posteriorized’). Conversely, based on a revision of the Cretaceous stem-zygopteran Congqingia rhora Zhang, 1992 and on data on the extant Chalcolestes viridis Van der Linden, 1825, the morphology of the basal complex in the total-group of Zygoptera is best explained by the hypothesis that the forewing configuration integrally replaced that of the hindwing (i.e., that the latter was ‘anteriorized’). A hypothetical model closely fitting the observed configurations is proposed, involving two modules, resulting from the duplication of a hypothetical primary module, and evolving independently (i.e., being paralogues), controlling the basal complex configuration and retaining the capacity to be activated in either wing pair. The merits of our proposal shall be further tested in light of the morphology of fossil taxa of the ‘anisozygopteran’ assemblage, it may actually contribute to dismantle, and, in parallel, thanks to the growing body of genomic data on Odonata. This case echoes those of arches in jawed vertebrates and whorls of angiosperm flowers, both involving paralogous structures modelled by paralogous developmental genes.