High resolution quantitative analysis of assemblages of planktonic foraminifera of the mid-latitude DSDP site 525A of the last 700 kyr of the Maastrichtian showed that there are distinct changes in relative species abundance which correlate with changes in ocean temperatures and surface to deep temperature gradient as inferred from oxygen and carbon isotopes. There are two groups of species, one of which increased in relative abundance during the warming of intermediate waters as recorded in benthic foraminifer Anomalinoides acuta, the other of which decreased in relative abundance during the warm interval then increased in abundance in the last 100 kyr of the Maastrichtian when both sea surface and intermediate water temperatures decreased. Mineralogical data and examination of specimens show that there was little dissolution of calcite and little recrystallization in the samples from this core so that isotopic signatures are probably primary. Mass ratio of the >149 mu m size fraction to the entire washed sample with calcite and detrital composition of the sample shows that the relative abundance of large, keeled forms likely primary signals rather than an artificial enrichment due to selective dissolution. The faunal trends do not demonstrate that the foraminiferal populations were declining towards a mass extinction due to environmental changes. Decreased cumulative species richness in the terminal cooling at the end of the Maastrichtian is not necessarily indicative of a stressed population in a terminal decline because it was recorded in species that were rare and at abundances lower than the statistical confidence limit. The faunal data does not demonstrate that the population would have recovered to the state it were in before the end-Maastrichtian warming event had the boundary event not occurred. An impact event would have found a population a foraminifera which were in a state of flux, possibly enabling a more severe extinction in those populations than would have otherwise occurred.