Abstract:

Analysis of the morphological characteristics of dental fossils is crucial for reconstructing the phylogenetic classification and evolutionary framework of orangutans. However, the fossil orangutan specimens from southern China have not been subjected to such research in this regard. This paper reports newly discovered orangutan teeth from the Dushanshang Cave site. Using morphological analysis methods for dental fossils, it attempts to construct a systematic classification and evolutionary framework for orangutans.

The Dushanshang Cave site is located in Yonglong Village, Linfeng Town, Tiandong County, Baise City, in the western part of Guangxi Zhuang Autonomous Region. The cave entrance faces northwest. Inside, the cave is 1~5 m wide and approximately 55 m long. The cave runs east-west overall. The entrance sits at an elevation of 236 meters above sea level, with the ground level outside the entrance approximately 16 m below. In 2012, the Guangxi Natural History Museum collaborated with the Tiandong County Museum to excavate this cave site. Prior to systematic excavation, researchers established Test Pit T1 approximately 50 meters from the cave entrance based on the preservation and distribution of deposits at Dushanshang Cave. After clearing disturbed surface deposits, excavation proceeded in 10-centimeter horizontal layers from top to bottom. Sediments from each layer were systematically collected and dry-sieved outside the cave using a 4 mm mesh to recover smaller fossils. The final excavation depth of T1 approximately 130 cm.

In addition to orangutan fossils, over 500 mammal tooth fossils were discovered at Dushanshang Cave. Representative mammal species include the Ailuropoda milanoleuea daconi, Stegodon orientalis, Elephas maximus and Megatapirus augustus. Based on comparisons with mammal faunas from different periods of the Quaternary in southern China, the Dushanshang Cave mammal assemblage has been tentatively dated to the Late Middle Pleistocene.

By encoding the morphological traits of the upper premolars and molars and employing correspondence analysis combined with classical hierarchical cluster analysis, we compared orangutan specimens from the Dushanshang Cave with fossils of the genus Langsonia and Pongo from northern Vietnam, as well as with extant P. pygmaeus. The results indicate that the morphological variation range of the Dushanshang Cave specimens not only exceeds that of the relevant groups from northern Vietnam but also shows significant distinctions from extant orangutans. Considering their dental dimensions and geological age, we assign them to P. weidenreichi. Further scoring and analysis of morphological traits from additional dental fossils will help refine the classification system and clarify the evolutionary relationships of orangutan fossils in southern China.

Key words: Pongo, Dushanshang Cave, Middle Pleistocene, classification and evolution, correspondence analysis