Jaw-Muscle Biomechanics in Primates

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With National Science Foundation support, Dr. Christopher Vinyard and collaborators will determine how the jaw-closing muscles function during chewing and biting in three model primate species. Physical anthropologists maintain an enthusiastic interest in how the primate feeding apparatus works and how it has evolved over the past 65 million years. Research on living primates describing the patterns of jaw-muscle activity and bone deformation in the skull during chewing has played a decisive role in developing our current understanding of how the feeding apparatus works. Furthermore, these experimental data have been fundamental to adaptive and evolutionary interpretations of primate and human evolution. Despite the advances offered by experimental studies of primate feeding, anthropologists still lack key information on the biomechanics of primate jaw-closing muscles during chewing. Building on previous research, this project aims to describe the biomechanics of the jaw muscles during chewing in a representative New World capuchin monkey (Cebus apella), Old World macaque monkey (Macaca fascicularis) and African galago (Otolemur crassicaudatus). Specifically, data will be collected on the timing and relative magnitude of jaw muscle activity via electromyography (EMG) in each species. Length changes in these muscles during chewing will be quantified using sonomicrometry technology. Combined analysis of EMG and sonomicrometry data will demonstrate whether jaw muscles are shortening, lengthening or contracting without changing length when active. Bone deformation will be recorded in areas of the skull adjacent to these muscles using strain gauges to estimate the force created by a contracting muscle. Data on length changes and force production for a muscle will be combined to estimate the work (i.e., force x length change) and power (work/time) of the jaw-closing muscles during chewing. Finally, these experimental data characterizing jaw-muscle biomechanics will be compared to jaw-muscle fiber architecture, fiber type and jaw form among these species. The proposed research will generate new information on how jaw muscles contract and do work during feeding in representatives from three major primate groups. This novel data will help anthropologists understand how primates use their jaw muscles to create force and move their jaws. Furthermore, because experimental data are essential to describing form-function relationships, this data will have broad implications for understanding how jaw-muscle fiber architecture, fiber type and jaw form relate to jaw-muscle function in primates. Finally, by comparing results from representatives of three major primate groups, these data will facilitate the testing of several hypotheses relating to primate chewing function and evolution. An important broader impact of this project involves training students through integrating education and research. Promotion of student learning and training through active participation will be emphasized in this project. Because experimental research skills involving animals can only be mastered through interactive apprenticeship and these opportunities are relatively rare, this project will provide a significant educational resource for physical anthropology. Additionally, this project will promote collaboration among three U.S. universities. Finally, the data collected on jaw-muscle function will benefit society by providing important basic science information for medical research focusing on human temporomandibular joint and myofascial pain disorders.