Coupled patterns of foraminiferal species richness and mega-climatic change across the Eocene-Oligocene transition

The Eocene-Oligocene transition (EOT) is the turning point of Earth’s Cenozoic climate, during which it stepped into the current “icehouse” state. The absence of a high-resolution, global, evolutionary timeline has limited understanding of the linkages between marine biodiversity and this environmental change. Here, we present a new 28-Myr-long foraminiferal species-richness history with an average temporal resolution of ~26 kyr based on a global dataset and quantitative stratigraphic method, CONOP. A significant richness decline accompanied the EOT, eliminating a great number of foraminifera species. The extinction events in planktonic foraminiferal (PF) and larger benthic foraminiferal (LBF) near the EOT appear to be associated with the combination of a rapid decrease in deep ocean temperature, a eustatic sea-level fall and a positive carbon isotopic excursion. In contrast, the much longer richness decline of small benthic foraminifera (SBF) across the EOT occurred in two phases: the first coincided with turnover of marine primary producers, and the second appears to have been temporally coincident with Afar-Arabian LIP activity, which led to expansion of oceanic anoxia and euxinia. Thus, mega-climatic changes are reflected in the species richness of foraminifera during the Eocene-Oligocene “warmhouse-icehouse” transition.