TECHNICAL NOTE - MODELING PRIMATE OCCLUSAL TOPOGRAPHY USING GEOGRAPHIC INFORMATION-SYSTEMS TECHNOLOGY

Most functional analyses of primate tooth form have been limited to li near or area measurements. Such studies have offered but a limited gli mpse at differences in occlusal relief among taxa. Such differences in dental topography may relate to tooth function and, so, have consider able implications for the inference of diet from fossil teeth. In this article, we describe a technique to model and compare primate molars in three dimensions using Geographic Resources Analysis Support System (GRASS) software. We examine unworn lower second molars of three exta nt hominoids with known differences in diet (Gorilla gorilla, Pan trog lodytes, and Pongo pygmaeus), and two fossil forms, (Afropithecus turk anesis and Dryopithecus laietanus). First, we obtained approximately 4 00 landmarks on the occlusal surfaces of each tooth using an electroma gnetic digitizer. Raster ''terrain models'' of occlusal surfaces were then created by interpolation of the coordinate data. We used GRASS te rrain analysis automated techniques to quantify the volumes and slopes of individual cusps. We also used the GRASS watershed technique to id entify the volume of liquid that would accumulate in each tooth's basi n (a measure of basin area), and the directions and intensity of drain age over the occlusal surface. In sum, GRASS shows considerable potent ial for the characterization and comparison of tooth surfaces. Further more, techniques described here are not limited to the study of teeth, but may be broadly applicable to studies of skulls, joints, and other biological structures. (C) 1998 Wiley-Liss, Inc.