Insect Mouthparts: Ascertaining the Paleobiology of Insect Feeding Strategies

Abstract

One of the most intensively examined and abundantly documented structures in the animal world is insect mouthparts. Major structural types of extant insect mouthparts are extensive, consisting of diverse variations in element structure within each of the five mouthpart regions—labrum, hypopharynx, mandibles, maxillae, and labium. Numerous instances of multielement fusion both within and among mouthpart regions result in feeding organs capable of ingesting in diverse ways foods that are solid, particulate, and liquid in form. Mouthpart types have a retrievable and interpretable fossil history in well-preserved insect deposits. In addition, the trace-fossil record of insect-mediated plant damage, gut contents, coprolites, and insect-relevant floral features provides complementary data documenting the evolution of feeding strategies during the past 400 million years. From a cluster analysis of insect mouthparts, I recognize 34 fundamental mouthpart classes among extant insects and their geochronological evolution by a five-phase pattern. This pattern is characterized, early in the Devonian, by coarse partitioning of food by mandibulate and piercing-and-sucking mouthpart classes, followed by a rapid rise in herbivore mouthpart types for fluid- and solid-feeding during the Late Carboniferous and Early Permian. Mouthpart innovation during the Late Triassic to Early Jurassic added mouthpart classes for fluid and aquatic particle-feeding. This ecomorphological expansion of mouthpart design was associated with the radiation of holometabolous insects, especially Diptera. The final phase of mouthpart class expansion occurred during the Late Jurassic and Early Cretaceous, with addition of surface-fluid-feeding mouthpart classes that subsequently became important during the ecological expansion of angiosperms. Conclusions about the evolution of mouthpart design are based on the mapping of phenetic mouthpart classes onto (ideally) cladistic phylogenies of lineages bearing those same mouthpart classes. The plotting of phenetic and associated ecological attributes onto baseline phylogenies is one of the most important uses of cladistic data.