Meeting Abstract
The mandible of most mammals is comprised of two hemimandibles that are united anteriorly at a symphyseal joint. Although mobile symphyses, as opposed to fully ossified and fused symphyses, are the most common symphyseal morphology across Mammalia, the function of the joint during feeding remains unclear for the vast majority of species. Here, XROMM was used to quantify the degrees of freedom of movement of each hemimandible with respect to the skull (i.e., translations along and rotations around the anteroposterior axis, the dorsoventral axis and the mediolateral axis) in 3 carnivoran species with unfused mandibular symphysis: Mephitis mephitis (skunk), Mustela putorius furo (ferret), Procyon lotor (raccoon). Movements are also evaluated relative to the phases of the gape cycle. The classic phases of the gape cycles are observed in all species (fast-closing, power stroke, slow-opening and fast-opening), although the power stroke is not always distinguishable in each cycle. Cycle duration, and thus chewing frequency, is similar, but phase durations vary significantly between species. Not surprisingly, dorsoventral rotation of both hemimandibles at the temporomandibular joint (pitch) producing jaw depression and elevation dominate chewing movements. Rotation about the anterior-posterior axis (roll) is observed, with maximum roll resulting in eversion of the alveolar process occurring during jaw closing. Some anterior-posterior translation (i.e., protraction retraction) of each condyle occurs, but there is no rotation around the dorsoventral axis (yaw), contrary to what has been observed in species with fused mandibular symphyses. In the species examined, the unfused symphysis may allow independent movements of the hemimandibles to facilitate alignment of the teeth during fast-closing and occlusion during the power stroke.
