Molar size and shape variations among Asian colobines

Despite decades of research, little is known about morphometric differences within the dentition of Asian colobines. Although some differences, such as the M 3 hypoconulid, are often cited as distinct among genera, no comprehensive assessment has been made. The objectives of this study were to document size and shape differences in third molars in eight Asian colobine genera, including Kasi , Nasalis , Presbytis , Pygathrix , Rhinopithecus , Semnopithecus , Simias , and Trachypithecus , and to quantify length differences for all molars in order to understand the potential impact of an occlusal surface area that includes the hypoconulid. To achieve these objectives, the most extensive survey yet published of Asian colobine dentition was conducted. Differences within and among genera for continuous and categorical variables were analyzed using descriptive statistics, chi‐square, t ‐tests, and post hoc comparisons. Results indicate that species of Presbytis differ from all other Asian colobines in both the size and shape of the maxillary and mandibular third molars. Specifically, M 3 of Presbytis is relatively shorter in length and less likely to exhibit a hypoconulid optimally positioned for occlusion with M 3 . Moreover, Presbytis expresses concomitant changes in the maxillary third molar such as absence of a distal shelf and/or a distal cusp with separated crests. We conclude that shape and size changes impact the molar size sequence patterns of Presbytis , setting this genus apart from all other Asian colobine taxa. These differences may reflect variation in overall body size, dietary adaptation, and phylogeny. Am J Phys Anthropol, 2004. © 2004 Wiley‐Liss, Inc.