Morphometric analysis of fossil hylobatid molars from the pleistocene of southern China

Abstract

This study investigates the morphological variation and taxonomic affinities of 28 fossil gibbon molars from eight newly discovered Pleistocene cave sites in the area of Chongzuo, Guangxi Zhuang Autonomous Region, China. A recent descriptive analysis demonstrated that these fossil teeth form a uniform group that can be assigned to a single species of Nomascus. In this contribution, a twodimensional morphometric approach is employed to examine the Chongzuo specimens in comparison with a large sample of extant hylobatids, as well as with previously reported hylobatid dental remains from the Pleistocene of China. Buccolingual and mesiodistal measurements and crown outline areas reveal that the Chongzuo molars correspond most closely with Nomascus and, to a lesser extent, Hoolock. Crown shape was investigated using elliptical Fourier analysis. Our results show that the Chongzuo specimens fall in most cases either within the range of variation of extant Nomascus to the exclusion of all other hylobatid genera, or their distance from the cluster represented by the Nomascus sample is relatively small. Similarly, the Mahalanobis distances for crown shape show a trend towards smaller morphological distances between the Chongzuo specimens and Nomascus, followed by Hoolock and Hylobates. The Chongzuo molars are also morphometrically distinct from Bunopithecus sericus, but fall within the range of overlap of other Pleistocene hylobatid dental remains from southern China. The balance of evidence indicates that the Chongzuo teeth can be attributed to cf. Nomascus. The fossil teeth are sufficiently distinct from those of extant Nomascus that they may represent an extinct species.