Middle Pleistocene Orangutan Fossil From Ganxian Cave,Tiandong County,Guangxi,South China And Its Significance Of Evolution

Ganxian cave,located at Bubing Basin,Tiandong County,Guangxi Zhuang Autonomous Region,south China,was found and excavated in 2008 and 2018 by Prof.Wang Wei and his research team.As a result,this site yielded rich mammal fossils,including Pongo teeth.The characteristics of the mammalian assemblage is similar to that of middle Pleistocene faunal assemblages of south China.Paleomagnetic results of sediment analysis indicate that the relative age of the deposition is in Brunhes normal polarity ehron.Biostratigraphical,paleomagnetic and U-series results indicate that age of Ganxian fauna can be constrained in late Middle-Pleistocene.The purpose of this paper is to study the evolution of orangutan in Asia by means of the analyses of dental morphology and metrics of those of modern and fossil orangutans from Asia in different time.On basis of the observation of fossil teeth of Pongo from Ganxian,they are morphologically similar to those of the extant and fossil species of Pongo.Given their metric comparison and survival time,the Ganxian sample can be assigned to Pongo weidenreichi.There is a general trend for dental crown size decrease from the Early Pleistocene(about 2.0 Ma)to extant populations,but it is by no means a neat linear decrease through time.The I1,P3 and m1 show a continued reduction in dental size from Early Pleistocene to present.The P4 s tend to become larger from the Early Pleistocene to the Middle Pleistocene and then becoming smaller.The M1 s were similar in size in the Early and Middle Pleistocene and then decreases from the Middle Pleistocene to present.The dimension of M2 s decrease from the Early Pleistocene to present-day.However,there was fluctuation in dental size of M2 s from the late Early Pleistocene to the Middle Pleistocen.The dimension of M3 s vary during Early Pleistocene,and then reduce from the late Early Pleistocene to present day.The dimension of i2 s tend to increase from the Early Pleistocene to the Late Pleistocene,and subsequently decrease up to extant species.The dimensions of crown are varying during the Pleistocene,including Male c,i1,p3,m2 and m3.The I1,P4,M2,male c,p3,m1 and m2 appear to more hypsodont through time,nevertheless,the i1 is not so remarkable.The P4 and m1 become more hypsodont from Middle Pleistocene to present day.The M1 and i2 become more hypsodont from Early Pleistocene to Late Pleistocene,but they become less hypsodont from the Late Pleistocene to present.So far,the Ganxian is one of the well-dated cave site in south China,providing a good opportunity to discuss the faunal variation,as well as the evolution of orangutan in Pleistocene.The many orangutan fossils are placed in a more rigorous and consistent chronological framework,which makes the evolutionary trends of the genus clarify.