Abstract
Being implied in flight, mimetism, communication, and protection, the insect wings were crucial organs for the mega diversification of this clade. Despite several attempts, the problem of wing evolution remains unresolved because the basal parts of the veins essential for vein identification are hidden in the basivenal sclerites. The homologies between wing characters thus cannot be accurately verified, while they are of primary importance to solve long-standing problems, such as the monophyly of the Palaeoptera, viz. Odonatoptera, Panephemeroptera, and Palaeozoic Palaeodictyopterida mainly known by their wings. Hitherto the tools to homologize venation were suffering several cases of exceptions, rendering them unreliable. Here we reconstruct the odonatopteran venation using fossils and a new 3D imaging tool, resulting congruent with the concept of Riek and Kukalová-Peck, with important novelties, viz. median anterior vein fused to radius and radius posterior nearly as convex as radius anterior (putative synapomorphies of Odonatoptera); subcostal anterior (ScA) fused to costal vein and most basal primary antenodal crossvein being a modified posterior branch of ScA (putative synapomorphies of Palaeoptera). These findings may reveal critical for future analyses of the relationships between fossil and extant Palaeoptera, helping to solve the evolutionary history of the insects as a whole.
Highlights
Despite recent advances, the monophyly of the group Palaeoptera remains controversial, mainly because of the antiquity of this group rendering the molecular analyses uncertain[1,2,3], and the fact that one of its major components, the Palaeodictyopterida are strictly fossil and mainly known by the wings[4]
Such examples are known like a palaeodictyopteran Mazonopterum wolfforum Kukalová-Peck and Richardson, 1983, or a typically neopteran architecture of basivenal sclerites demonstrated on Paoliida[10,11]
ScP is emerging from a basivenale ScB independent of RB, and the so-called ‘costal margin’ results from the fusion of three different veins, viz. subcostal anterior (ScA) emerging at the very base of ScB and appressed to it for a long distance (Fig. 1c,d, Suppl. movies 7–9), a concave vein CP, and a convex vein CA that is in an anterior position relatively to CP (Suppl. movies 2–5); CA has a long course between ScB and CB, makes an anterior curve and ends into basal part of CB; CP emerges from the mid part of the posterior side of CB
Summary
We combine the precise observations of basal wing structures in an extant taxon studied with 3D tomography with the study of a well-preserved fossil. Separated and convex ScA with maybe a posterior branch forming a crossvein between anterior margin and ScP occurs in some members of the palaeodictyopterid Megasecoptera, viz. Eubrodia dabasinskasi Carpenter, 1967 or Brodia priscotincta Scudder, 1881 (Brodiidae)[26] This group characterized by remarkably petiolate wings is considered as a close relative of Palaeodictyoptera due to a specialized type of mouthparts in form of a rostrum as synapomorphy for all Paleodictyopterida. This special shape of ScA is a putative synapomorphy of Odonatoptera with Ephemeroptera, and (at least some) Palaeodictyopterida, to be confirmed by the reconstruction of an extant mayfly wing using the same CT-scan technique Another striking feature is the presence of well-separated concave CP discernable between ScA and anterior wing margin, which was omitted in the original description of Zygophlebia[27]. This character is a putative synapomorphy of Odonatoptera with the Palaeodictyoptera, to be searched in the Ephemeroptera and the Neoptera too
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