Abstract:

In the past century, abundant fossil orangutans have been successively discovered in southern China, ranging from the Early Pleistocene to Late Pleistocene. However, few early Middle Pleistocene fossil orangutans with precise absolute dating have been reported in southern China. To date, no scholar has provided a detailed morphological description of early Middle Pleistocene fossil orangutans, thereby limiting our exploration of scientific questions such as the evolution of orangutans in southern China during the Pleistocene. Here, we report the recovery of 34 fossil teeth of orangutans from Yanli Cave 2 in Chongzuo, Guangxi, southern China. We further compare them to samples of fossil orangutans (i.e., Pongo weidenreichi, Pongo devosi, Pongo duboisi, Pongo palaeosumatrensis, Pongo javensis, and Pongo sp.) from the Pleistocene and to extant orangutans (i.e., Pongo pygmaeus and Pongo abelii) from Southeast Asia. The Yanli Cave 2 Pongo teeth are 19.3% larger on average than those of extant Pongo (P. pygmaeus and P. abelii). The Yanli Cave 2 Pongo teeth are larger in overall size than those of P. devosi, P. palaeosumatrensis, and P. javensis, comparable to P. duboisi, and fall within the range of P. weidenreichi. The Yanli Cave 2 Pongo teeth differ from those of extant Pongo (P. pygmaeus) in having upper molars with a greater incidence of s trace of a lingual cingulum and upper and lower molars with a lower incidence of moderate to heavy wrinkling. The Yanli Cave 2 Pongo teeth differ from those assigned to P. devosi in having upper and lower incisors with an undeveloped or a weakly developed lingual pillar and lingual cingulum, upper molars with a lower incidence of a trace of a lingual cingulum, and upper and lower molars with a lower incidence of moderate to heavy wrinkling. Based on their dental size, and the presence of undeveloped or weakly developed lingual cingulum on the upper and lower incisors, a low frequency of lingual cingulum remnants on the upper molars, and a low frequency of moderate to heavy wrinkling on the molars, we assign the Yanli Cave 2 fossils to P. weidenreichi. Compared with orangutan fossils from other mainland Southeast Asia sites, the incidence of a trace of a lingual cingulum on the upper molars from Yanli Cave 2 is lower than P. weidenreichi and P. devosi from the middle and late Pleistocene. The result indicates that the morphological characteristics of orangutans in southern China may have changed during the early Middle Pleistocene. This research provides new scientific evidence for understanding the classification evolution of great apes in East Asia.

Key words: Orangutans, dental morphological characteristics, Middle Pleistocene, Yanli Cave 2, Guangxi of China