Studies on the origin og the fossil vertebrate faunas in the Ryukyu islands ant its international correlation

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Result of study on 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. 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. So long as result of excavations done in post five years in the Ryukyu islands, five diagnostically different stratigraphic levels containing Late Miocene to latest Pleistocene vertebrate fossils have been delinated in the islands. Among the fossil assemblages found in these five 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 named Imadomari-Akagimata assemblage and are considered to be immigrants from the latst Okiocene Renzidong fauna in Anhui Province 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. Among the vertebrates in the Imadomari-Akagimata assemblage, the archetypal derr (=Cervus (Metacervulus) new species A) arrived to the islands from the continent as a progenitor and its descendants were dflourished in the islands during the Pleistocene together with another cervid and large terrestrial tortoise (=Manouria). These taxa became complately extinct at the end of Pleistocene (ca. 15,000 years B.P.), after the formation of many morphotypes. It can be said that other animal in this assemblage may serve as the progenitors of the present mammals, reptiles, and amphibians living in the Ryukyu Islands.