Studies on a process of formation of an island-form mammalian faunas in the Nansei Islands

1)为了明确土加喇海峡的地质时代和历史，从地层学、磁性地层学和古生物学的角度对种子岛更新世增田组进行了详细的研究。考虑到裂变径迹年龄，该地层可与早更新世的松山倒转期后半期至布鲁赫正常期前半期的磁性带相对应。2）增田组的一种蛙化石与现生活在吐噶喇海峡以南奄美群岛的蛙化石相一致。3）对1939年在宫古岛发现的象臼齿化石进行了详细的重新鉴定，并将其与日本列岛和台湾早更新世沉积物中常见的猛犸象原型--Mammuthus armeniacus shigensis进行了鉴定。这一结果表明，宫古岛与大陆的陆地连接发生在早更新世晚期。笔者试图通过对这些岛屿中鹿化石的身体比例的演变趋势进行研究，并建立陆栖脊椎动物向冲绳岛迁移的可能顺序。通过对南西岛哺乳动物群化石和现生动物群的分析，提出南西岛与大陆的陆缘可划分为早更新世第一阶段、中更新世晚期第二阶段和晚更新世第三阶段。

1) To clarify the geologic age and a history of the Tokara Channel, the Pleistocence Masuda Formation in the Tanegashima Island was studied in detail basis on the stratigraphy, magnetostratigraphy and the paleontology. Taking account the fission-track ages, this formation can be correlated with the Early Pleistocene magnetozone ranging from the later half of the Matuyama Reversed Epoch to the early half of the Brunhes Normal Epoch.2) A fossil frog from the Masuda Formation was identified with the species now living in the Amami Islands, south of Tokara Channel. From this discovery, it may be inferred that Osumi and the AmamiIslands might be connected at the Early Pleistocene.3) A molar of fossil elephant discovered at 1939 from the Miyako Island was re-examined in detail and was identified with an archetypal mammoth-Mammuthus armeniacus shigensis which is commonly occurred from the Early Pleistocene deposits of the Japanese Islands and Taiwan. The result imply that the land connection between the Miyako Island and the continental area has taken placed at the late Early Pleistocene.4) Based on the morphological and statistical studies on fossil deers from the Nansei Islands, the writer tried to scrutinize the evolutionary trend of the body proportion of fossil deer in the islands and to establish the probable order of migration of terrestrial vertebrates to the Okinawa-jima.5) Based on the analysis on the fossil-and living mammalian faunas and its geologic ages, following three stages of the land connection of the Nansei Island to the continent are proposed, namely, Stage I of the Early Pleis tocene, Stage II of the late Middle Pleistocene and Stage III of the Latest Pleistoce.