Odonatopteran Approaches to the Challenges of Flight: Convergence of Responses Subject to a Common Set of Morphological Constraints

Abstract

Effective flight capacity is a crucial survival attribute of volant animals. Several vertebrate clades have acquired gliding capabilities and at least three of them independently acquired powered flight. Contrastingly, wings were probably acquired only once by pterygotan insects. Despite this, insects have developed a great variety of structural approaches that have diversified their collective flight capacity. Flight was a key contributor to their diversification during the Late Carboniferous (at least 330 Ma), and flying insects have remained the most diverse animal clade since then. Among pterygotans, representatives of the superorder Odonatoptera, which includes the extant Odonata, have developed impressive performance associated with the highly complex morphological structure of their wing venation. Some venation patterns, such as the nodus, discoidal complex, and arculus, were acquired only once, whereas others have been convergently acquired several times. One example of a pattern acquired more than once is the sclerotized pterostigma, convergently appearing in the Permian Protanisoptera and its sister group, the Discoidalia, these comprising the modern Odonata. All odonatopterans with broad wings were confronted by a major problem, that of ‘how to strengthen the basal third of the wing’ to prevent it from breaking longitudinally. At least eight different convergent ‘solutions’ have been ‘adopted’ that have resulted in the incorporation of structures oriented perpendicular to the main axis of the wing. Additionally, several clades within the Odonatoptera have convergently developed petiolated wings, adapted for flying in cluttered environments. The width and length of the petiole can vary greatly, with the most impressive ones being those of the ‘giant’ Permian-Triassic Triadophlebiomorpha. This great morphological disparity represents ‘variations on a theme’ of the already complex wing venation established by the first Carboniferous odonatopterans. It is possible that some of the ‘solutions’ arrived at by extinct clades allowed for performance that was more effective than that of modern odonatans. Many of these groups flourished and co-existed with the ancestors of modern taxa for millions of years. Extant odonatans have been adopted as models for the bio-mimetic development of small drones. The wing patterns of extinct clades should also be investigated for their potential for bio-mimetic inspiration and application.