Early Pleistocene Ground Beetles(Coleoptera:Carabidae) from the Ookui Formation in Nagano Prefecture, Central Japan, and their Biogeographical and Paleoenvironmental Significance.

Abstract

Abundant fossil beetles were obtained from the Lower Pleistocene Ookui Formation in Kitamimaki-mura, Kitasaku-gun, Nagano Prefecture, Central Japan. These fossils are composed of ground and aquatic beetles, such as Carabidae, Dytiscidae, Hydrophilidae, and Donaciinae of Chrysomelidae. Several fossils of ground beetles are identified with three interesting species, Hemicarabus maeander, Apotomopterus maacki, and Chlaenius gebleri. Among them, H. maeander is not distributed in Honshu where the fossil occurred, but can be found in Hokkaido, Chejudo, Sakhalin, N. E. China, Mongolia, East Siberia, and North America at the present time. The fossil finding indicates that the widely and continuous distributional range of this species seemed to become discontinuous, and extinct in Honshu after the Early Pleistocene. Thus, this species can be considered as a geographic relict species in Honshu during the Pleistocene. The paleoenvironment of the Upper member of the Ookui Formation based on beetle fossils seems that there were mainly low moor of reeds accompanied with areas of still water. These beetle assemblages, especially including H. maeander and C. gebleri, suggest presence of low moor which is similar to those found in Hokkaido during the Upper member of the Ookui Formation deposited.