On March 25, a research team from The Institute of Cultural Heritage of Shandong University (ICH-SD) published a research paper entitled " Middle Pleistocene Pongo from Ganxian Cave in Southern China with implications for understanding dental size evolution in orangutans" in Journal of Human Evolution. This paper reports a recent discovery of late Middle Pleistocene orangutan fossils from Ganxian Cave in Bubing Basin, Guangxi, Southern China, which provides essential evidence for exploring the origin and evolution of great apes in Asia. The first author of the paper is Liang Hua, a PhD student, and the corresponding authors are Dr Liao Wei and Prof. Wang Wei at ICH-SD.

Figure1. Ganxian Cave. A) Landscape of the Ganxian Cave. B) The entrance of the Ganxian Cave. C) Plan view of the Ganxian Cave showing the location of the test pits.

Figure2. A) Test Pit B after excavation. B) Flowstone above the sediment of Test Pits. C) Photos of the sampled carbonate from the flowstone in Layer 1. D) Pongo tooth in situ. E) The composite stratigraphy of Ganxian Cave. Abbreviations: PM = paleomagnetic polarity chron; ESR =electron spin resonance.

Among all the primates, extant great apes are our nearest living relatives. Their evolutionary studies are important parts for human origin. Orangutans are the only extant great apes in Asia, where they are currently restricted to the tropical forests of Sumatra and Kalimantan. However, fossil records indicate that they had widely distributed in Southern China and Southeast Asia during the Pleistocene period.

In this study, authors described the fossil teeth from Ganxian Cave and compared them metrically to samples of fossil and extant Pongo from Southeast Asia. Based on the overall dental size, a high frequency of lingual cingulum remnants on the upper molars, and a low frequency of moderate to heavy wrinkling on the molars, the Ganxian fossils are assigned to a known species (Pongo weidenreichi). The age of the Ganxian fauna was constrained between 362 ± 78 ka and 168.9 ± 2.4 ka, by U-series and coupled ESR/U-series dating methods, representing one of the securely dated late Middle Pleistocene sites in southern China so far. This study also confirmed that dental size reduction of Pongo occurred principally during the Early and Middle Pleistocene. From the Middle Pleistocene to the Late Pleistocene, all teeth (except the upper third premolar) show little change in occlusal area, indicating that the size of these teeth remained relatively stable over time. The evolutionary trajectory of the Pongo dentition through time may be more complex than previously thought.

Figure 3. Representative teeth of Pongo from Ganxian Cave.

Figure 4. Box-and-whisker plots of the occlusal areas of the postcanine teeth from the Early to Late Pleistocene.

Journal of Human Evolution (JCR: SSCI Q1) is the leading professional journal in paleoanthropology, which is dedicated to publishing high-quality articles in the field of human origins and evolution worldwide.