Patterns of Evolution in the Feeding Mechanism of Actinopterygian Fishes

Abstract

SYNOPSIS. Structural and functional patterns in the evolution of the actinopterygian feeding mechanism are discussed in the context of the major monophyletic lineages of ray-finned fishes. A tripartite adductor mandibulae contained in a maxillary-palatoquadrate chamber and a single mechanism of mandibular depression mediated by the obliquus inferioris, sternohyoideus, and hyoid apparatus are primitive features of the Actinopterygii. Halecostome fishes are characterized by having an additional mechanism of mandibular depression, the levator operculi—opercular series coupling, and a maxilla which swings anteriorly during prey capture. These innovations provide the basis for feeding by inertial suction which is the dominant mode of prey capture throughout the halecostome radiation. A remarkably consistent kinematic profile occurs in all suction-feeding halecostomes. Teleost fishes possess a number of specializations in the front jaws including a geniohyoideus muscle, loss of the primitive suborbital adductor component, and a mobile premaxilla. Structural innovations in teleost pharyngeal jaws include fusion of the dermal tooth plates with endoskeletal gill arch elements, the occurrence of a pharyngeal retractor muscle, and a shift in the origin of the pharyngohyoideus. These specializations relate to increased functional versatility of the pharyngeal jaw apparatus as demonstrated by an electromyographic study of pharyngeal muscle activity in Esox and Ambloplites. The major feature of the evolution of the actinopterygian feeding mechanism is the increase in structural complexity in both the pharyngeal and front jaws. Structural diversification is a function of the number of independent biomechanical pathways governing movement.