Hajime Taniuchi, Hokkaido University, Department of Natural History Science, Sapporo, Japan, Takeshi Kuritani, Hokkaido University, Department of Earth and Planetary Sciences, Sapporo, Japan, Tetsuya Yokoyama, Tokyo Institute of Technology, Tokyo, Japan, Eizo Nakamura, Okayama University, Okayama, Japan and Mitsuhiro Nakagawa, Hokkaido Univ, Sapporo, Japan