Abstract A total of 12 ostracodes species belonging to 10 genera are reported for the first time from the lower Pliocene Takikawa Formation in Takikawa City, Hokkaido, northern Japan. The ostracode fauna of the formation includes both cryophilic and circumpolar species. Cryophilic species are Baffinicythere robusticostata Irizuki, 1996, Neomonoceratina tsurugasakensis (Tabuki, 1986), and Yezocythere hayashii Hanai and Ikeya, 1991, and circumpolar species are Palmenella limicola (Norman, 1867) and Semicytherura mainensis (Hazel and Valentine, 1969). The co-occurrence of cryophilic and circumpolar species suggests that the marine environment was strongly influenced by extremely cold water masses. The species diversity and equitability of the fossil ostracode assemblages indicate that the depositional topography was the inner area of a bay. One new genus and one new species, Woodeltia sorapuchiensis new genus new species, are described. This new genus occurred in a temperate environment in Japan, in the early Miocene. In the early Pliocene, Woodeltia adapted to cold environmental conditions in Hokkaido. We hypothesize that Woodeltia sorapuchiensis is an important species for Woodeltia , showing the group’s adaptation to cold environments and migration to the coast of North America. UUID: http://zoobank.org/144937f5-1161-42a9-9cc1-5c652cdb88b3
Mukai et al. (Wed,) studied this question.