Jaw-muscle function and the origin of primates

Anthropologists studying primate chewing have focused on the origins and evolution of the masticatory apparatus of anthropoids and humans. We know far less about the functional morphology and evolution of the masticatory apparatus in the earliest euprimates (e.g., Jablonski, 1986). A more complete understanding of masticatory apparatus function in the earliest primates would greatly benefit studies of chewing behavior in both strepsirrhines and haplorhines. We begin addressing this shortcoming in this chapter by asking, "To what extent do treeshrews share similar jaw-muscle activity patterns during chewing with living primates?" We use the small, nonprimate mammal, Belangers treeshrew (Tupaia belangeri), as an extant model of jaw-muscle activity during chewing, or mastication, in early euprimates. By comparing living primates to this treeshrew, we can infer whether the origin of primates involved significant changes in jaw-muscle activity patterns during chewing. Because we can make some basic functional links between jaw-muscle activity patterns and jaw form, our results will aid future interpretations of masticatory apparatus function from jaw form in living and fossil primates.