Uplift of the Hengduan Mountains on the southeastern margin of the Tibetan Plateau in the late Miocene and its paleoenvironmental impact on hominoid diversity

The southeastern margin of the Tibetan Plateau has a number of well-known Late Miocene localities that have yielded fossil hominoids belonging to Lufengpithecus and Khoratpithecus. These localities provide critical evidence about the evolutionary history of hominoids, including their response to environmental changes associated with uplift of the Tibetan Plateau. Here we present magnetostratigraphic dating of the Baoshan hominoid locality in Yunnan, southwestern China, which, based on preliminary biochronological evidence, was previously assumed to be the youngest known Miocene hominoid locality in Eurasia. Paleomagnetic investigations yield three normal and three reversed magnetozones, which can be best correlated, in conjunction with biostratigraphic constraints, to Chrons C3n.4n to C3Ar. The Baoshan hominoid is derived from a horizon correlated with the lowest part of C3r, having an estimated age of ~6.0 Ma. This indicates that the Baoshan hominoid is slightly younger than L. cf. lufengensis from Zhaotong, dated to ~6.2 Ma, and L. lufengensis from Lufeng, dated to ~6.9–6.2 Ma. Our results, coupled with previously published magnetochronology, indicate that hominoids occurred in Southeast Asia from the latest Middle Miocene to the terminal Miocene (~13–6 Ma). The period after 6 Ma coincides with the uplift of the Hengduan Mountains, especially the Gaoligong Mountain. We propose that the Late Miocene uplift of these N-S oriented mountains on the southeastern margin of the Tibetan Plateau created a barrier to the warm and moist Indian monsoon from the west, and this led to a cooler and drier climate in the southeastern margin of the Tibetan Plateau. This paleoenvironmental change potentially had a profound impact on the diversity of the hominoid community in southwestern China and Southeast Asia.