Determining past oceanographic change often involves organic or inorganic geochemical proxies, however, there is a wealth of information available from examining alterations in the assemblages of marine biota. Microscopic fossils (foraminifera, nannofossil, diatoms, radiolarians) are abundant in deep sea sediments and can provide a record of paleoceanographic change. Marine cores from the International Ocean Discovery Program and its predecessors allows examination of how different groups responded through time, and in particular their reaction at climatic perturbations. Changes in the marine biota may involve the extinction of species or groups of species that can tell us about alterations in their habitat. It can also comprise the enhanced abundance of a particular species, or a group, for a short interval of time (acme events). The dwarfing of organisms is increasingly becoming recognised as a response to environmental stress, however, I will show several intervals in the Cenozoic where a species became much larger for a short interval of time. Different plankton groups respond in different ways. For example, a major turnover in both calcareous (planktonic foraminifera) and siliceous (radiolarians) zooplankton occurred at the middle/late Eocene boundary about 38 Ma. New analysis of the nannofossil assemblages indicates a relatively muted response, and demonstrates the contrasting sensitivity to environmental change in these plankton groups. This talk focuses on Cenozoic ocean drilling records where the marine microfossils respond in sometimes mysterious ways, with particular focus on the Eocene, Oligocene and Miocene.