THE MANDIBLES OF SOME ADULT GROUND BEETLES - STRUCTURE, FUNCTION, AND THE EVOLUTION OF HERBIVORY (COLEOPTERA, CARABIDAE)

The structure of carabid and other adephagan mandibles can provide information about the mechanics of feeding in these beetles and about the major features of carabid and adephagan evolution. Homologies among mandibular features are proposed, based on a transformation series for adult mandibles from plesiotypic cupedid-like structure to derived conditions characteristic of herbivorous carabids in the subtribe Harpalina. Terms for mandibular parts are revised so that all ridges and teeth are referred to as such. The following terms are introduced: superior and inferior terebral ridges, superior and inferior retinacular ridges, supraterebral ridges, anterior and posterior occlusal grooves, and basal face. Masticatory function is elucidated for the mandibles of adult Euryderus grossus (Say) in which the mandibles shear food matter in both a horizontal and a vertical plane, as well as compacting food into a bolus that is forced posteriorly into the buccal cavity. Many of the features of E. grossus mandibles are characteristic of other herbivorous carabids, but not all such taxa show derived mandibular structure.