Dissertation

The form-function complex of the primate masticatory apparatus

Fitton, Laura C

2008

Overview

Craniofacial morphology varies considerably between primate species with many aspects of structural variation occurring within the masticatory apparatus. These variations in masticatory fonn are frequently attributed to differences in diet however elucidating the relationship between masticatory form and function is complex. This study combines the techniques of shape analysis in a comparative study of the primate masticatory apparatus with three-dimensional biomechanical modelling of primate jaw mechanics. The relationship between masticatory form and function is investigated within a subfamily ofprimates, the Cercopithecinae. Species within this group display a range of masticatory forms, inhabit a wide range of environments, have varying diets and share close phylogenetic relationships making them an ideal group to investigate the relationship between structure and function. Using the techniques of geometric morphometrics a shape analysis was conducted in which variations within the masticatory forms of the Cercopithecinae were quantified. Functional predictions of observed shape differences were made and considered in light of known environmental and ecological factors with particular emphasis on dietary specialisations and fall back foods. The results of the shape analysis indicate that differences in body size, strata utilisation, and diet appear to play a major role in structuring adult morphological diversity within and among the Cercopithecinae. Many of the shape differences associated with an increased body size appear to reflect the selective pressures of increased predation risk, including increases in the length ofthe jaw and canine teeth. These morphological traits are associated with the production of a large gape and are hypothesised to be functional adaptations to the use of canines as weapons. Other major shape differences apparent between the Cercopithecinae were those associated with the proportion of leaves and fruit in the diet. The highly frugivorous Mandril/us species possessed features associated with increasing gape and retractile motions of the mandible ideal for incision of large fruits. By contrast the dietary specialist Theropithecus gelada possessed features associated with increasing the efficiency of food breakdown and muscle force production, necessary to process their more abrasive foodstuff (i.e. grasses).

• Publisher: ProQuest Dissertations & Theses
• Subject: Morphology