Paleoceanographic events and deep-sea ostracodes.

Eight recognized or theorized paleoceanographic events during the past 70 million years were tested against changes in the global deep-sea benthic ostracode fauna. Two events, the sudden Cretaceous-Tertiary boundary event at 66 million years ago and the more gradual 40-million-year event (formation of the psychrosphere), show up most dramatically. Before the 40-million-year event, ostracodes freely radiated into the deeper water regions but were provincial. The development of thermal stratification isolated these deep-water taxa, mostly the survivors of the Cretaceous-Tertiary boundary event, which adapted to a new, free-flowing but more frigid ecosystem and spread rapidly throughout the world.