Implication of Mammal Fauna for the Quaternary Geohistory of the Japanese Islands

Abstract

This article discusses some problems on the Quaternary mammal fauna of the Japanese islands which were raised in the course of the Quaternary Map Project of the Japan Association for Quaternary Research. The characteristics of the present Japanese mammal fauna are enumerated as follows: a rich number of species per area, a high degree of endemism, and a large number of indigeneous forest dwellers in the fauna. Among the many endemic species, the following are important in holding the key to the origin of fauna: Glirulus (Rodentia)-Urotrichus and Dymecodon (Insectivora) of the Honshu block, and Pentalagus (Lagomorpha)-Diplothrix and Tokudaia (Rodentia)-Mayailurus (Carnivora) of the Ryukyu Islands. The origin of the present mammal fauna of the Japanese Islands is assumed to date back to the Late Miocene or Pliocene time. It is also interesting that the Japanese fauna have been consistently composed of humid forest inhabitants since the time of its origin.
Next the formation of the fauna is discussed. The first appearance of the extant species was possibly at the later time of the Middle Pleistocene. Therefore, the formation of the present mammal fauna probably began at the same time, 130-200 thousand years before the present. Subsequently, after the high sea level of the Last Interglacial, most of the pre-existing species were replaced by the extant species (with the exception of some peculiar forms) and disappeared before the advent of the final phase of the Last Glacial. Immigrants from the continent to the Honshu block and the Ryukyu Islands have scarcely been recognized since the early Late Pleistocene. Immigration from the south, which was formerly considered, viz of Siva-Malayan and Sino-Malayan forms, now seems unlikely, because it seems appropriate in some parts in explaining the faunal changes of the Japanese Quaternary mammals to adopt the vicariance hypothesis instead of the disperasl hypothesis.