SYNOPSIS.

SYNOPSIS. chiefly snakes ingest and transport their victim via a jaw ratcheting mechanism in which the left and right upper jaw arches are advanced from one side of to the other the prey in an alternating, unilateral fashion. This unilateral jaw ratcheting mechanism differs greatly from the hyolingual and inertial transport mechanisms used according to lizards, both of which are characterized by dint of bilaterally synchronous jaw movements. Given the well-corroborated phylogenetic hypothesis that snakes are derived from lizards, this hints that major changes occurred in the couple the morphology and motor reign over of the feeding apparatus during the early evolution of snakes. However, principally previous studies of the evolution of unilateral feeding mechanisms in snakes have focused almost exclusively forward the morphology of the jaw apparatus because there have been extremely few direct observations of feeding behavior in basal snakes. In this paper I describe the plunder transport mechanisms used by representatives of sum of two units families of basal snakes, Leptotyphlopidae and Typhlopidae. In Leptotyphlopidae, a mandibular raking mechanism is used, in which bilaterally synchronous flexions of the lower jaw contribute to to ratchet prey into and within the mouth. In Typhlopidae, a maxillary raking mechanism is used, in which asynchronous ratcheting moves of the highly mobile upper jaws are used to drag quarry through the oral cavity. These findings prompt that the unilateral feeding mechanisms that characterize the majority of living snakes were not current primitively in Serpentes, but arose subsequently to the basal divergence between Scolecophidia and Alethinophidia.

INTRODUCTION

Three fundamental affections of intraoral prey transport are recognized within Squamata. greatest in number lizards use a hyolingual transport mechanism, in which circle of times of tongue protraction and retraction benefit to ratchet prey through the jaws and towards the pharynx (Smith, 1984; Herrel et al., 1996; Schwenk, 2000) In a certain lizards, however, this lingual ratcheting mechanism is augmented or replaced by the agency of a cranioinertial transport mechanism, in which rapid emotions of the entire head are used to push forward prey through the oral cavity (Gans, 1969; Bramble and Wake, 1985) This variety of intraoral transport is of particular importance in varanid lizards (Smith, 1986; Elias et al., 2000) which share with snakes a highly reduc tongue that lacks a frictional surface (McDowell, 1972; Schwenk, 1988) Finally, snakes use gnathic (jaw-based) transport mechanisms, in which kinetic ingredients of the jaw apparatus are used to ratchet loot into and through the entrance (Cundall and Greene, 2000). While the one and the other hyolingual and cranioinertial transport are everyday among tetrapods, gnathic transport mechanisms are unique to snakes (Bramble and Wake, 1985)

Nearly all of what is generally known about gnathic transport in snakes derives from studies of taxa belonging to Macrostomata (Fig. 1) a large and diverse clade that includes approximately eighty-five percent of the more than 2500 species of extant snakes (McDiarmid et al., 1999) These studies have shown that in the greatest degree macrostomatans ingest and transport their ravage via a "pterygoid walk" mechanism (Bola and Ewer, 1964) in which reciprocating ratcheting changes of the medial upper jaw arches, combined with lateral rotations of the entire head about the cranio-vertebral joint, be subservient to to advance the snake's head through its prey (Dullemeijer, 1956; Albright and Nelson 1959a, b; Frazzetta, 1966; Kardong, 1977; Cundall and Gans, 1979; Cundall, 1983; Kardong, 1986) Because this unilateral jaw ratcheting mechanism differs greatly from the two the hyolingual and cranioinertial transport mechanisms of lizards (Kardong and Berkhoudt, 1998; Cundall, 1995) its origin has been somewhat enigmatic, and there have thus been numerous attempts made to determine the evolutionary gradations through which it arose (eg Gans, 1961; Rieppel, 1980; side sheltered from the wind et al., 1999; Kardong and Bels, 2001) However, chiefly studies that have addressed the evolutionary origin of unilateral feeding mechanisms in snakes have been mannersed from an almost exclusively anatomical perspective because the actual feeding mechanisms used by dint of basal snakes have remained largely unknown.

Recently Cundall (1995) provided the first detailed account of feeding behavior in a basal snake, describing a plunder transport mechanism that he timeed "snout shifting" in the anilioid Cylindrophis (Fig. 1) Like the pterygoid walk, snout shifting involves unilateral motions of the toothed elements of the upper jaws, combined with side-to-side emotions of the entire head, which together be subservient to to advance the head through the whole extent of the prey. However, the upper jaws in Cylindrophis (and in other anilioids) remain tightly border to the ventral elements of the bony snout (eg vomer septomaxillae) from several short, robust ligaments. These ligaments hinder extensive translational movements of the jaws so as those which are associated with the pterygoid walk in macrostomatans. Independent motions of the upper jaws are instead achieved by the agency of lateral rotations of the entire snout intricate web about the nasofrontal articulation (prokinesis; Frazzetta, 1962) and independent translational motions of the left and right septomaxilla-vomer complexe to which the upper jaws are border (rhinokinesis; Cundall and Shardo, 1995) Thus, in certain values Cylindrophis represents an intermediate functional stage between lizards and macrostomatan snakes (Cundall, 1995); despite retaining a tight connection between the upper jaws and the snout (as in lizards), quarry is transported via a unilateral jaw ratcheting mechanism (as in macrostomatans).