Late Cretaceous (Campanian) Shallow‐Marine Ostracods From Northeastern Margin of Asia—Palaeoenvironment and Biogeographical Significance

ABSTRACT Information on the Late Cretaceous (Campanian) shallow‐marine ostracods found along the eastern margin of the Northwest Pacific remains less known, although this palaeogeological situation is critical for understanding regional marine endemism. Six new species, including one new genus— Hobetsucythereis ohtatsumei gen. et sp. nov., Cytherella yezoensis sp. nov., Cytherelloidea hetonaiensis sp. nov., Haplocytheridea maedai sp. nov., Cythereis hokkaidoensis sp. nov. and Cythereis kimun sp. nov.—are described in this study. The palaeobathymetry of the Hakobuchi Formation, estimated from the relative diameter of the fossil eye tubercle of H . ohtatsumei , was 150 ± 20 m. The vertical light attenuation coefficient during deposition (0.108 ± 0.018) is comparable to that of the Atlantic coast, the Arctic and highly productive regions of the South Atlantic Ocean. The Campanian ostracod province is categorised into eight (sub)provinces, many of which are separated by deep seas and/or large rivers. [Correction added on 10 February 2026, after first online publication: The Abstract has been updated to remove “Cytherelloidea popetensis sp. nov.” and to add “Cythereis kimun sp. nov.” after “Cythereis hokkaidoensis sp. nov.”].