Cranial morphometric pattern of gibbon in mainland and island Southeast Asia

Abstract

Southeast Asian archipelago is the home of a wide range of endemic gibbon species. While human cranial morphometic variation based on insularity and provinciality is extensively studied, little is known about the pattern on other insular non-human hominoid species. Two gibbon species of Hylobates lar and Hylobates agilis crania found in both mainland and island were examined to be compared to all gibbon species throughout Southeast Asia. The exterior outline of 22 lateral and 12 dorsal three-dimensional homologous landmarks were digitized on 141 crania. The landmark data were first subjected to generalize Proscustes Analysis, followed by principal component analysis. Wireframe diagram demonstrates that compared to crania of the mainland, the lateral crania of the island in both hylobates species displays a generally convex anteromedial corner on parietal bones with the shift of the junction of coronal and sagittal sutures (BRG) anteriorly and the inion (INI) ventrally. The dorsal view exhibits the strong shift of orbital surface of sphenoid bone (SFT) medially on the island crania. This investigation contributes as the preliminary study of insularity of non-human primate of Southeast Asia.