Prey Transport Mechanisms in Blindsnakes and the Evolution of Unilateral Feeding Systems in Snakes1

SYNOPSIS. Most snakes ingest and transport their prey via a jaw ratcheting mechanism in which the left and right upper jaw arches are advanced over the prey in an alternating, unilateral fashion. This unilateral jaw ratcheting mechanism differs greatly from the hyolingual and inertial transport mechanisms used by lizards, both of which are characterized by bilaterally synchronous jaw movements. Given the well-corroborated phylogenetic hypothesis that snakes are derived from lizards, this suggests that major changes occurred in both the morphology and motor control of the feeding apparatus during the early evolution of snakes. However, most previous studies of the evolution of unilateral feeding mechanisms in snakes have focused almost exclusively on the morphology of the jaw apparatus because there have been very few direct observations of feeding behavior in basal snakes. In this paper I describe the prey transport mechanisms used by representatives of two families of basal snakes, Leptotyphlopidae and Typhlopidae. In Leptotyphlopidae, a mandibular raking mechanism is used, in which bilaterally synchronous flexions of the lower jaw serve to ratchet prey into and through the mouth. In Typhlopidae, a maxillary raking mechanism is used, in which asynchronous ratcheting movements of the highly mobile upper jaws are used to drag prey through the oral cavity. These findings suggest that the unilateral feeding mechanisms that characterize the majority of living snakes were not present primitively in Serpentes, but arose subsequently to the basal divergence between Scolecophidia and Alethinophidia.