Meeting Abstract
Identifying relationships between mandibular morphology and jaw kinematic variables is critical for understanding how diet relates to feeding system form. Variation in primate prognathism has been related to differences in gape, bite force, and mechanical advantage of the masticatory muscles, but do jaw movements covary with facial prognathism? We examined covariation between chewing cycle form and facial form in three craniofacially-variant species of primates—macaques (Macaca mulatta), baboons (Papio anubis), and capuchins (Sapajus apella). Reflective markers were coupled to the mandible and cranium and their three-dimensional movements were captured using a Vicon motion capture system at 250 frames per second. A geometric morphometric approach was used to analyze three-dimensional covariation between rhythmic jaw movements and facial form. Chewing cycles were standardized to 99 frames and registered to a common facial form and the three-dimensional residual motion sequences were compared to facial variation of each species using a two-block partial least squares analysis. The results indicate a significant covariation between gape cycle form and facial form, such that taxa with greater prognathism had smaller gape cycles with reduced vertical displacement but larger lateral displacement. We hypothesize that smaller gape cycles in subjects with greater prognathism reflect tradeoffs between mechanical advantage and gape, suggesting that primates modify their jaw movements to maximize the mechanical advantage of their masticatory muscles. This covariation also suggests that differences in craniofacial morphology can affect jaw kinematics during chewing, and possibly other aspects of feeding kinematics.
