鮮新世の北西太平洋からギルモアオットセイの初産出

概要

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A horizontal ramus of the right dentary with P_4 and M_1 referable to the extinct fur seal, Callorhinus gilmorei Berta and Demere, 1986,is described from the Dainenji Formation in the Futaba district, Fukushima Prefecture, northeastern Japan. The geologic age of the pinniped-bearing horizon within the Dainenji Formation in the Futaba district is reevaluated based on the detailed analysis of associated fossil diatom assemblages. The age of the uppermost D_4 facies of the Dainenji Formation in the Futaba district, which produced the dentary of the Gilmore fur seal, is estimated to be late Late Pliocene, approximately between 2.7 and 2.4 Ma. Since the Gilmore fur seal had been previously known only from the Late Pliocene of California and Mexico, the specimen from the Dainenji Formation is the first record of this species in the western North Pacific and documents the circum North Pacific distribution of Callorhinus species since at least the Late Pliocene.
1997-12-22