A new middle Miocene pliopithecid from Inner Mongolia, China

Abstract

In the nearly 80 years since the American Museum of Natural History Central Asiatic Expeditions first discovered fossil mammals in Inner Mongolia, subsequent paleontological research in the region has resulted in the recovery of extensive collections of Neogene mammals (Qiu et al., 2006). However, no primates have been found in this area, with the possible exception of one heavily worn M3 from Ertemte, described by Schlosser (1924) as Pliopithecus posthumus, but whose primate status has been questioned (see Harrison, 2005). During the past two decades, the discovery of several species of pliopithecids from the Miocene of China has contributed greatly to understanding the evolutionary history of this group. Pliopithecids are first represented in China by Dionysopithecus and Platodontopithecus from the late early Miocene of Sihong, correlated to w17e18 Ma (Harrison and Gu, 1999). During the middle Miocene, at w15 Ma, Pliopithecus sp. and Pliopithecus zhanxiangi are recorded at localities in Gansu Province and Xinjiang and Ningxia Hui Autonomous Regions (Harrison et al., 1991; Wu et al., 2003; Deng, 2003). Finally, Laccopithecus robustus, a crouzeliine pliopithecid, is known from the late Miocene (w6e7 Ma) of Shihuiba, Lufeng County, Yunnan Province (Wu and Pan, 1985; Pan, 1988; Pan et al., 1989). During a field excursion in 2006, a team led by the first author found a productive middle Miocene mammal locality in Siziwangqi, Inner Monglia, which has produced a large collection of fossil mammals, including one well-preserved upper molar of a pliopithecid. The tooth has a unique suite of morphological features that indicate that it belongs to a species that has not previously been recognized. In addition, it has several specializations that can be inferred to be synapomorphies linking the specimen to crouzeliines. This find extends the geographic distribution of pliopithecids in China, but also raises interesting questions about the ecology and environmental change in eastern Asia during the middle Miocene/late Miocene transition. These changes may have had an important impact on the biogeography and evolution of pliopithecids and their associated faunas.