Eocene ostracodes from Hahajima Island of the Ogasawara (Bonin) Islands, northwestern Pacific, and their paleobiogeographic significance in the West Pacific

Abstract

During the Eocene, Hahajima Island of the Ogasawara (Bonin) Islands of the Izu-Mariana Arc in the North Pacific was located near the present-day position of western Pacific Micronesia. We identified 17 Eocene ostracode species from the island, of which are new species and likely endemic to this island or to the West Pacific. These new species are systematically described herein and include: Costa matsumarui n. sp., Cytherelloidea ogasawaraensis n. sp., Havanardia ujiiei n. sp., Jugosocythereis nishii n. sp., Neonesidea boninensis n. sp., Schizocythere antiquimicronesiana n. sp., and Uroleberis hahajimaensis n. sp. The Eocene ostracode fauna has a higher rate of endemism than does the modern Micronesian fauna and contains Tethyan genera. These findings contradict a hypothesis that the Pacific fauna had a higher endemism rate after the Paleogene. The findings support another hypothesis that some genera invaded the Pacific from Tethys during the Paleogene. They suggest that West Pacific species did not disperse to the periphery of the Indo-West Pacific region during the Middle–Late Eocene. The “center of origin” hypothesis cannot be applied to Middle–Late Eocene marine ostracode biogeography.