ミャンマー中部の新第三系の地質と動物相の変遷

Abstract

Since 2002, Primate Research Institute of Kyoto University, Japan, and the Department of Archaeology of the Ministry of Culture, Myanmar, have jointly carried out the paleontological investigations at the late Neogene sediments, including the Upper Pegu Group and Irrawaddy sediments, that are widely distributed along two large rivers, Ayeyarwady and Chindwin Rivers, in central Myanmar. Here we examined the transition of the mammalian fauna in Myanmar, mainly based on four later Neogene localities in central Myamar: Thanbinkan (late Middle Miocene), Yenangyaung (early Late Miocene), Chaingzauk (latest Miocene/early Pliocene), and Gwebin (Late Pliocene). As a result, at least two turnover events of terrestrial mammal fauna were recognized. The first faunal turn over likely occurred around the boundary between the Middle and Late Miocene. Many primitive proboscideans, including a deinotheriid (Prodeinotherium), an amebelodontid (Amebelodon) and several gomphotheriids (Protanancus, Anancus and unidentified taxon), which have been discovered from Thanbinkan, are not discovered from the Yenangyaung locality. The second turnover likely occured in the middle Late Miocene: several middle to large-size terrestrial mammals including Tetraconodon, Hipparion, Bramatherium and Brachypotherium, all of which were common animals in the Yenangyaung fauna, were replaced by new members, such as Sivachoerus, Hexaprotodon, Rhinoceros and Stegodon, which characterize the Chaingzauk and/ or Gwebin faunas. These turnover events were probably influenced by the environmental changes during the early Late Miocene in central Myanmar. However, we have discovered very few small sized mammal fossils from the Neogene sediments in central Myanmar to date, and most large-sized fossils donated to the temples and/or to the public museums lack the exact locality data. Additional specimens including not only large- but also middle- to small-sized mammals would shed light to the faunal transition in the Late Neogene mammal fauna in central Myanmar.