Boughner, Julia Cathryn; (2002) Dental and mandibular growth in Papio and Pan. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A fundamental quandary in oral development is how the jaws and the dentition co-develop synchronously, and how each may or may not influence the other's development. The aim of this study was to identify any differences in mandibular growth that might underlie known differences in the timing of permanent molar tooth initiation that exist between baboons (Papio anubis) and great apes (Pan paniscus, Pan troglodytes). The principal hypothesis was that greater space availability, or some difference in mandibular growth, explains intertaxon differences in molar initiation times. This was tested by comparing mandibular and molar tooth development between genera (Papio n=52 and Pan) and sister taxa (bonobos n=44 and chimpanzees n=60). Radiographic, linear measurement, and three-dimensional (3D) co-ordinate landmark data were taken from individuals of these three taxa representing a broad range of developmental ages. Multivariate statistical shape analyses demonstrated that the mandibles of baboons and the apes develop across statistically different ontogenetic trajectories of shape change. Observed changes in mandibular shape were supported and in some instances explained by bivariate analyses of mandibular and molar tooth proportions. No statistical differences in mandibular shape change were observed between the ape species. Multivariate shape analysis of molar crown formation failed to confirm statistical differences between any of the taxa. Qualitative analysis of these 3D data demonstrated subtle and inconclusive intergenus differences among adjacent intermolar distances. The pattern of intermolar spacing was virtually constant throughout development for all molar crowns in all taxa. Space available distal to successive molar crowns was equivalent among taxa, but perhaps slightly greater in the baboon. The poor correlation between mandibular proportion and both intermolar spacing and 3D molar development pattern failed to confirm the principal hypothesis. Rather, the mandible and dentition are a good example of two developmentally autonomous systems that have evolved in complement under strong selection pressures.

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