Meeting Abstract

P1.50  Sunday, Jan. 4  Ontogeny and fusion of the mandibular symphysis in camelids STOVER, K.K.; WILLIAMS, S.H.*; Ohio University; Ohio University willias7@ohio.edu

Ontogenetic ossification, or fusion, of the mandibular symphysis in mammals is thought to be associated with weaning and the shift to an adult diet. In particular, symphyseal fusion may be biomechanically advantageous for strengthening and/or stiffening the symphysis against routine masticatory loading. Recent work on alpacas (Lama pacos), which exhibit ontogenetic symphyseal fusion, demonstrate significant differences in jaw-muscle recruitment patterns and symphyseal loading between pre-weaned and adult alpacas. However, the morphological context for these differences, and in particular the ontogeny of symphyseal fusion, is not fully understood. Here, we describe the morphology of the pre-fused symphyseal joint and characterize the pattern of ossification of the mandibular symphysis in camelids using osteological and fresh specimens and CT scans of live animals. Symphyseal development is then related to various masticatory parameters, including EMG and bone strain data from alpacas. The pre-fused symphysis of neonate and infant camelids consists of two relatively flat symphyseal surfaces. Ossification of the joint begins rostrally, with some individuals fusing first along the lingual portion and others along the labial portion. In some individuals, minor bony interdigitations develop in the caudal and labial region of the symphyseal joint prior to full fusion. Fusion is complete between 6 and 8 months. Thus, full fusion precedes or is coincident with occlusion of the first molar yet significantly precedes the onset of adult chewing motor patterns and symphyseal bone strain patterns. Although the pattern of fusion cannot be directly related to observed strain patterns, we cannot rule out that forces generated during mastication in pre-weaned individuals influence ossification of the symphyseal joint.