Similarities between Planktonic and Larger Foraminiferal Evolutionary Trends through Paleogene Paleoceanographic Changes

The Paleogene evolutionary records of planktonic foraminifera and larger benthic foraminifera show parallel patterns in development that may, in part, reflect changes in nutrient flux to surface waters. Following the terminal Cretaceous extinctions, faunas were dominated by a few cosmopolitan opportunistic species. More specialized k-strategists in both groups diversified during the Paleocene, dominating into the early Eocene, consistent with he globally mild climatic regime and probable limited rates of nutrient flux to surface waters. High-latitude cooling intensified in the middle Eocene, promoting diversification of less specialized taxa characteristic of cooler and deeper waters, higher latitudes, meridional upwelling zones, and boundary currents. Geographic ranges of warm-water taxa diminished and fragmented, yet many species survived. Thus, global diversities during the middle Eocene were the highest in the Cenozoic. As cooling and increased rates of nutrient flux further intensified in the late Eocene, extinction rates of warm-water planktonic and larger benthic species exceeded origination rates of cooler water and less specialized forms, so diversity dropped to intermediate levels where it remained through the late Eocene and Oligocene. Previous observations that planktonic foraminiferal faunas dominated by warm-water taxa are often replaced by cool-water faunas, even though oxygen isotopes only recorded relatively minor cooling, can be reconciled by the explanation that the biotic communities responded to changes in trophic resources and euphotic habitats that accompany the temperature reduction, as well as to temperature change itself