Structural and functional integration within the primate masticatory system during development
The following thesis explores developmental changes to several key components of the masticatory system within a model primate species (Macaca fascicularis). In study 1, significant changes were observed in both architectural and biomechanical properties during development. Fiber lengths, muscle mass and physiologic cross-sectional area (PCSA) all scaled with positive allometry relative to both jaw length and condyle-molar length during development; meanwhile, temporomandibular joint (TMJ) height also scaled with positive allometry against both measurements of mandibular length. Study 2 introduces a technique for the non-destructive determination of architectural variables, using a textural recognition algorithm. Strong agreement between this technique and gross dissection was observed for both components of the masseter complex; however, the more complex temporalis muscle diverged in the measurement of muscle fiber lengths (and consequently, PCSA). In study 3, the functional impact of these developmental changes was measured using a series of biomechanical models, simulating masticatory motions within individuals of different ages. Older, larger-bodied individuals demonstrated increases in both bite force and gape potential. As such, adults of both sexes display an improved ability to consume larger and more mechanically resistant food items, mirroring observed behavioural shifts within this species towards the consumption of larger and more mechanically resistant foods with increasing age. These findings demonstrate that changes in masticatory anatomy occur alongside developmental shifts in dietary ecology towards an increase in the consumption of larger and more mechanically resistant foods, and an increase in the prevalence of wide-gape display behaviours. The anatomical configuration of the primate masticatory system is therefore observed to closely reflect its dietary and social niche, adapting during life to meet changing functional demands.