6 - Ontogeny and function of the masticatory complex in Gorilla: Functional, evolutionary, and taxonomic implications

Summary

Introduction

The classic studies of Coolidge (1929) and Groves (1967, 1970a, b, 1986; Groves and Stott, 1979), coupled with more recent investigations (Uchida, 1996, 1998; Taylor, 1998a, b, 1999, 2002), have revealed considerable variability in the cranium, mandible, and dentition among subspecies and even geographic populations of gorillas (Albrecht et al., Leigh et al., Stumpf et al., this volume). Historically, investigators have tended to emphasize the taxonomic implications of this variation (Coolidge, 1929; Groves, 1967, 1970a) and with good reason, as a well-founded taxonomy clearly forms the basis for meaningful studies in other important fields, including morphology, behavioral ecology, and genetics. While there have been some attempts to draw functional inferences from differences in craniomandibular and dental morphology among gorilla subspecies (Vogel, 1961; Groves, 1970a, b; Uchida, 1996, 1998; Taylor, 1998b, 1999, 2000), nevertheless the nature and patterning of variation in jaw form among gorilla subspecies remains unresolved.

I examine masticatory form and function in gorillas to assess whether gorilla subspecies differ predictably in morphology as a function of dietary specialization. I focus particularly on the expected pattern of morphological differentiation in Gorilla based on the degree to which these taxa differ in degree of folivory versus frugivory. I use an ontogenetic, allometric approach in an explicitly phylogenetic context to evaluate whether differences among subspecies can be principally attributed to extrapolation or truncation of inherited patterns of ontogenetic allometry (Shea, 1995), or to derived dissociations of ancestral allometries.