Bulletin of the Mizunami Fossil Museum

Monograph of the Mizunami Fossil Museum No. 7

Marine molluscan fossils of Cenozoic Japan are studied from the viewpoints of paleobiogeography and phylogeny.

Followings are clarified.

1. Temporo-spatial distribution of marine molluscan faunas from Paleogene to the present around the Japanese Islands is synthesized as shown in Fig. 1.

2. Tropical faunas decreased their scales of temporo-spatial distribution with the times (Fig. 2).

3. The lower sublittoral to bathyal faunas in Cenozoic Japan have wide geochronological and geographical distributions.

4. Bioserial changes of molluscs are divided into five types. They are represented by extinct genera, extinct species, long-living species, and species with bioserial changes among different areas and in limited area.

5. Extinctions of molluscan species are remarkable between Paleogene and Miocene, and between Miocene and Pliocene.

6. Some of tropical and boreal species are long-ranged and they belong to the long-living species or to the species with bioserial changes in different areas.

7. Some of species 1iving in the lower sublittoral to bathyal zone are chronologically long ranged species.

8. Species with bioserial changes are common in the Japonic type species.

9. Seas around the Japanese Island and their environs have changeable environments influenced by tropical and boreal currents. Bioserial changes seem to be takes places in these changeable environments.

10. Speciations might be due to geographical or ecological isolations caused by environmental changes.