Lab-based electromyographic (EMG) studies of primate jaw-muscles have been integral for understanding primate masticatory function. However, because jaw-muscle activity patterns are directly influenced by food mechanical properties, lab studies of primate feeding utilizing foods not consumed in the wild do not arguably reflect ecologically-relevant behaviors. In this project, we take the lab to the field to study jaw-muscle activity patterns in wild and free-ranging mantled howling monkeys (Alouatta palliata) in Costa Rica. A custom-made EMG system allows us to record the EMG activity from 8 jaw muscles at a time while the animals are freely ranging in their natural habitat. These data facilitate the interpretation of jaw-muscle function in the context of environmentally-dictated selection pressures that primates experience. We are able to compare jaw-muscle activity patterns within individuals feeding on different foods within and between wet and dry seasons and relate these differences to food mechanical properties. Because we can record over EMG activity over multiple days, we can accurately calculate daily jaw-loading cycles, which may provide some information on the extent to which cyclical loading shapes skeletal morphology in the skull.

Collaborators: Dr. Chris Vinyard (NEOUCOM), Dr. Ken Glander (Duke Univ.), Dr. Mark Teaford (Johns Hopkins Univ.), and Dr. Max Deffenbaugh. Funded by the Ohio University Research Committee and the National Science Foundation.