北太平洋の鮮新世セイウチ類(哺乳類 : 食肉目)とその古生物地理

概要

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Four fossil tusks belonging to the tribe Odobenini DEMERE, 1994b, in the subfamily Odobeninae of the family Odobenidae, are described from Pliocene rocks in Japan. The previous hypothesis, that the tusked walruses originated in the North Atlantic in the latest Miocene and that the Recent walrus genus Odobenus evolved in the North Atlantic and entered into the North Pacific via the Arctic Ocean in the Middle Pleistocene, are revised on the basis of the succession of occurrences of the tusked odobenids in the North Pacific from Late Miocene until Recent time. It suggests that the tusked odobenids might have evolved in the North Pacific Ocean during the late Late Miocene and never disappeared from the North Pacific. Likewise, the genus Odobenus might have originated in the North Pacific and immediately spread out into the North Atlantic through the Arctic Ocean during the Late Pliocene on the basis of their earlier records in the North Pacific.
1995-12-22