Morphology of the lower jaw and suspensorium in the Texas blindsnake, Leptotyphlops dulcis (Scolecophidia: Leptotyphlopidae)

Abstract

Slender blindsnakes (Leptotyphlopidae) are known to use a unique feeding mechanism that involves rapid flexions of the tooth-bearing lower jaw. However, the morphology of the leptotyphlopid jaw apparatus has remained poorly studied due to the extremely small size of these snakes. Here I present a detailed description of the bones, cartilages, and ligaments of the lower jaw and suspensorium in a representative leptotyphlopid, Leptotyphlops dulcis, based on microanatomical studies of nearly 30 specimens prepared and examined in a variety of ways. The leptotyphlopid mandible is found to exhibit a complex mixture of symplesiomorphies shared with nonophidian squamates ("lizards"), synapomorphies shared with other snakes, and autapomorphies unique to Leptotyphlopidae. Most autapomorphies are functional correlates of the mandibular raking mechanism used by Leptotyphlops, primarily involving specializations of the intramandibular joint and the linkage between the suspensorium and the skull. Most notably, the quadrates are suspended via sliding articulations with the stapedes and do not articulate directly with the braincase. Posterior translation of the suspensorium at this loose, sliding articulation during jaw retraction may account for approximately one-third of the distance that prey are transported during each cycle of jaw flexion. This primary quadratostapedial articulation is believed to be unique among gnathostomes. Several anatomical features of the jaw apparatus suggest that Leptotyphlops evolved from more typical snake-like ancestors that: 1) had already lost the firm symphysis between the distal tips of the mandibular rami; and 2) had already evolved a high degree of upper jaw mobility.