Pleistocene Vertebrate Faunas in the Ryukyu Islands: Their Migration and Extinction

Abstract

Results of present studies on the stratigraphic levels and the paleontological analysis of terrestrial vertebrate fossils in the Ryukyu islands furnish valuable clues and considerations as to the history and age of animal migration from the continent to its neighboring islands. To date, four diagnostically different stratigraphic levels containing Late Miocene to latest Pleistocene vertebrate fossils have been delineated in the islands. Geological and paleontological data suggest that the area of the Ryukyu Islands has been repeatedly connected to the Asiatic Continent and each land connection has been followed by migration of characteristic terrestrial vertebrates from the continent.
Among the fossil assemblages found in these four different stratigraphic levels, those from Level 2 (Early Pleistocene) are known to occur in shallow marine deposits underlying the Early to Middle Pleistocene Ryukyu Group. They are considered to be immigrants from either the latest Pliocene Renzidong fauna (Jin & Zheng, 1998; Huang, 1998; Jin et al., 1999) in Anhui Province or the Wushan hominid fauna (Huang et al., 1991) in Sichuan Province, both located in Central China, during the second land connection. This assemblage may be regarded as the oldest post-Miocene fauna and might include the ancestors of the Pleistocene fossil and living endemic terrestrial vertebrate faunas of the Ryukyu islands.
Another important species of fossil assemblage of terrestrial vertebrates in the islands is closely associated with the latest Pleistocene fissure and cave deposits developed within the Ryukyu Group or coeval terrace deposits (Level 4). These assemblages are considered to be mixed faunas that migrated from the Asian mainland to the islands during different periods of land connection in the past. Terrestrial vertebrate fossils from this level include large mammal (deer) and giant tortoise that became extinct at the end of the latest Pleistocene. However, descendants of other animals including mammals, amphibians and reptiles, are still living in the islands forming characteristic insular endemic fauna.