Craniometric Analysis of Two Primate Species from Sri Lanka: Macaca sinica and Trachypithecus vetulus

Abstract

Anthropoid primates In Sri Lanka belong to the group of Old World Monkeys in the family Cercopithecidae. The more omnivorous macaques belong to the sub-family Cercopithecinae and the folivorous two langur species to Colobinae, respectively. There are marked external morphological differences between the macaque species and two langur species. However, no studies have been conducted to determine the differences from their skeletal morphology. This study attempts to determine the species variation using standard craniometrical measurements. Ten macaque and purple-faced langur crania and 8 macaque and 10 langur mandibles were measured housed at the Department of Sociology and Anthropology University of Sri Jayewardenepura, at the National Museum Colombo and from a private collection. Fifteen cranial and 9 mandibular measurements were taken using a digital sliding caliper. In the cranium, there are statistically significant differences in the muzzle length, nasal breadth, nasal height, piriform height, piriform breadth and inter orbital breadth between these two species. Macaque cranium has a longer muzzle, greater upper facial height and a wider long nose than the langurs. However, the langur cranium has a wider inter orbital distance and narrow piriform aperture than the macaques. In the mandible, there are statistically significant differences between bicondyle breadth, bigonial breadth, bimental eminence breadth and height of ramus. Langur mandibles are taller and wider than macaques. When considering the teeth, both species have bilophodont teeth; nevertheless langur teeth have higher cusps than macaques. This is directly related to their dietary specialization and is used to distinguish between Cercopithecines and Colobines. These cranial and mandibular measurements and dental morphology are very important for the identification of different primate species from the bones excavated from prehistoric cave sites in Sri Lanka.