Homologisation of the anterior articular plate in the wing base of Ephemeroptera and Odonatoptera

Abstract

In the search for the sister group of modern Ephemerida, we used the evolutionary groundplan method to identify synapomorphies in wing articulation. The evolutionary approach is necessary because post-groundplan wing adaptations have obscured the phylogenetically informative higher-level synapomorphies in modern Ephemerida, Odonata and Neoptera. Protowing-level sclerites are recognisable fragments of the first limb-derived pleuron, arranged in eight rows above the pathways delivering blood to the eight principal wing veins. Each row includes three sclerites (proxalare, axalare and fulcalare) which articulate with the basivenale (wing blood sinus). Over the course of the pterygote evolutionary history, many row-sclerites have assembled into clusters, plates, or processes, the composition of which can be most clearly recognised by comparison with ancestral Paleozoic fossils. The extant orders Ephemerida and Odonata (Palaeoptera: Hydropalaeoptera) share a derived anterior articular plate (AAP) composed of four fused sclerites (two axalaria and two fulcalaria) belonging to the precostal and costal rows. This plate represents a complex and unique synapomorphy. In Neoptera, precostal and costal fulcalaria are fused to basivenalia to form a humeral plate, and axalaria are obscured by the tegula. Palaeoptera include two subdivisions, extant Hydropalaeoptera and extinct Palaeodictyopteroida.