Review of the history of the deep-sea ostracod genera Abyssocythere Benson and Dutoitella Dingle, and their responses to Cretaceous - Cenozoic oceanic water-mass changes

Abstract

Abyssocythere and Dutoitella are extant benthic bathyal ostracod genera that evolved during Coniacian to Santonian/Campanian time from shallow-water progenitors around southeastern Africa. Their Late Cretaceous development was primarily in the South Atlantic, but during the Palaeogene they spread to the Indian and Pacific oceans. The establishment of the psychrosphere (late Eocene-mid-Oligocene) flushed populations of each genus from their central Atlantic cradles into the Pacific, presumably through the Panama Seaway, so that contemporaneous centres of evolution developed disjunct clades: A. trinidadensis and D. praesuhmi. The psychrospheric oceanic event defined temporal thermophyllic and cryophyllic populations of the two genera. Three Neogene ocean events appear to have affected several regionally-confined species, inter alia one of which entailed a counterflow migration of A. atlantica from the eastern Pacific back into the central Atlantic during the mid-Miocene. Modern distributions of Abyssocythere and Dutoitella are disjunct: in the Atlantic both genera occur south of approximately 40 degrees N (Dutoitella), and equatorial areas (Abyssocythere); in the Indian Ocean both are confined to the southern part; and in the Pacific, Abyssocythere is restricted to central and north-eastern areas, and Dutoitella to the west and northwest. Neither genus evolved species that were more than para-cosmopolitan: A. diagrenona (South Atlantic-Indian; Eocene-Oligocene), A. trinidadensis complex (central Atlantic-NW Pacific; Oligocene-Miocene), D. crassinodosa complex (South Atlantic-Indian; Eocene), and D. praesuhmi (north and central Atlantic-central Pacific; Oligocene-Miocene).