Although the relationship between skull form and function has been well studied in primates, the ways in which jaw muscle fiber architecture (such as fiber length and orientation) remodels and adapts to different feeding behaviors and diets have been rarely examined and remain poorly understood. Evaluating the bony and muscular systems together, this study examines the ways in which skull form and fiber architecture are functionally related to feeding behavior and diet. Results of this study will provide important information on how the jaw muscles and bony skull are functionally integrated to both produce and limit movement during feeding, and can be applied to studies reconstructing feeding behavior and diet in fossils.
This project begins with a comparison among three species of South American monkey (Callitrichidae, Primates). These monkeys have uniquely different feeding behaviors, but are otherwise characterized by similar diets. The contrast in feeding behaviors between these closely-related monkeys provides an ideal model to evaluate the significance of fiber architecture for muscle function. Specifically, common marmosets (Callithrix jacchus) feed on tree gums by opening their jaws widely (producing a wide jaw gape) and applying their anterior teeth to gouge the tree trunk or branch in order to stimulate the flow of gums. Cotton-top tamarins (Saguinus oedipus) and squirrel monkeys (Saimiri sciureus) also feed on gums, but unlike marmosets, these primates feed on gums that have already been extracted by insects or other mechanical damage to the tree. Through initial study of these three monkeys, the relationship between fiber architecture, skull morphology and feeding behavior is addressed through the following two specific objectives. First, fiber architecture of the superficial masseter and temporalis muscles is examined using gross anatomic, microscopic, and histologic techniques. The hypothesis is tested that the tree-gouging common marmoset has an architectural arrangement that facilitates the production of wide jaw gapes. Second, morphological data on the skull will be obtained to examine how skull structure is functionally and/or adaptively linked to different feeding behaviors. As part of the long-range goals of this project, fiber architecture and craniometric data on prosimian and anthropoid primates will be collected to evaluate the cranial correlates of fiber architecture. These data will be used to test whether bone proxies can be employed to accurately predict architectural parameters of muscle, and to evaluate how these parameters vary with changes in skull and body size.
The project has an important educational component that involves training and supporting undergraduate students in all aspects of this project. This work continues to support the Duke University Women's Initiative by encouraging undergraduate women in research and will also strengthen collaborative relationships among three academic institutions.
