Immigration of Mammals into the Japanese Islands during the Quaternary.

Abstract

Immigration of mammals during the Quater-nary is considered separately in three biogeo-graphic regions of the Japanese Islands: Hon-shu-Shikoku-Kyushu; Hokkaido; and the Ryu-kyu Islands. In Honshu-Shikoku-Kyushu, bio-stratigraphic studies of elephant fossils haverevealed the earliest appearances of three ele-phant species in Quaternary sequences, namely around 1.2-1.0 Ma for Mammuthus shigensis, around 0.5 Ma for Stegodon orientalis, and around 0.3 Ma for Palaeoloxodon naumanni. These appearances indicate their immigrationfrom the adjacent continent, and also suggest the formation of a land bridge which enabled the immigration. Since the immigration stage of P. naumanni, Honshu-Shikoku-Kyushu has been isolated from the Asian continent as well as from Hokkaido. In Hokkaido, fossil records are much scarcerthan in Honshu-Shikoku-Kyushu. Late Pleis-tocene mammals of Hokkaido are represented by only three large herbivores: P. naumanni, Mammuthus prinigenius, and Sinomegaceros yabei. Of these, P. naumanni and S. yabei immi-grated from Honshu-Shikoku-Kyushu, possibly around 0.3 Ma, while M. primigenius moved into Hokkaido from Siberia via Sakhalin dur-ing the late Late Pleistocene. In the Ryukyu Islands, Pleistocene fossil records are mostly restricted to those of the Late Pleistocene. The Late Pleistocene fauna in the northern part is dominated by endemic elements which immigrated from the continent possibly in the pre-Pleistocene period. The fauna in the southern part is composed of Late or Middle Pleistocene immigrants as well as much earlier immigrants.