KLEY, N.J.: The evolution of prey transport mechanisms in snakes

Three fundamental modes of intraoral prey transport are recognized within Squamata. Lizards use either hyolingual or inertial transport mechanisms, both of which involve bilaterally symmetrical jaw movements. In contrast, most snakes exhibit a unilateral jaw-ratcheting mechanism that is characterized by asymmetrical jaw movements. Given the well-corroborated phylogenetic hypothesis that snakes are derived from lizards, this suggests that major changes occurred in both the structure and motor control of the feeding apparatus during the early evolution of snakes. Previous studies of the evolution of feeding systems in snakes have focused primarily on morphological features that were believed to have facilitated the elaboration of unilateral transport mechanisms within alethinophidian snakes. Until recently, however, scolecophidian snakes have generally been excluded from such analyses, despite their intermediate phylogenetic position between lizards and other snakes. I used high-speed videography to study feeding mechanics in two families of scolecophidian snakes (Leptotyphlopidae and Typhlopidae). Leptotyphlopids were found to transport prey using a bilaterally symmetrical mandibular raking mechanism. Furthermore, the morphology of the leptotyphlopid jaw apparatus suggests that prey transport in these snakes is mediated primarily by hypoglossal rather than trigeminal musculature. In contrast, typhlopids generally used an asynchronous maxillary raking mechanism during intraoral transport. As in alethinophidians, protraction and retraction of the upper jaw arches in typhlopids are controlled largely by muscles of the constrictor internus dorsalis group. However, differences in morphology and feeding kinematics suggest that the asymmetrical jaw-ratcheting mechanisms of typhlopids and alethinophidians arose independently.