Stable isotope geochemistry of Gwebin mammalian fauna with implications for late Neogene paleoenvironmental changes in central Myanmar

To explore the paleoenvironmental changes in SE Asia during the late Neogene, we examined the stable carbon and oxygen isotope compositions of tooth enamel from mammals of the late Pliocene/earliest Pleistocene Gwebin area in central Myanmar and compared the results with those of the latest Miocene Chaingzauk mammals in Myanmar. The stable carbon isotope values (delta 13C) of Gwebin mammals indicate that they inhabited mosaic environment ranging from woodland to grassland. The relative abundance of C3-browsing versus C4-grazing bovids as well as other C3-consuming anthracotheriids, porcupine, rhinoceroses, suids, and stegodontids suggest the dominance of wooded environment. In central Myanmar, it is assumed that floral transition from C3 to C4 plants has occurred since the latest Miocene to Early Pliocene relating to the Himalayan Orogeny. However, stable isotope data at present indicate that paleoenvironment of central Myanmar did not change considerably in the Pliocene and served as a refugium for several forest/woodland dwellers at least until the early Pleistocene. The development of the proto-Ayeyarwady and proto-Chindwin drainage systems in the late Neogene of Myanmar induced the riparian environment, probably buffering against the rain shadow effect of the IndoMyanmar Ranges. The onset of the present day aridification in central Myanmar is probably related to the Middle to Late Pleistocene sea-level changes in SE Asian region, which have had a major impact on climate, vegetation and megafauna of SE Asia.