Rise and fall of rotaliid foraminifera across the Paleocene and Eocene times.

Rotaliids are one of the groups of larger foraminifera that quickly recolonized the shallow-water environments after the mass extinction at the end of the Cretaceous. Here we present a summary of the state of the art about their stratigraphic distribution and diversity across the Paleocene and Eocene epochs. Our data suggest that their differentiation at the genus level was very rapid and reached its maximum in the upper Danian SBZ2. Specific diversification, instead, culminated in the upper Thanetian SBZ4, with a second peak during the Cuisian (=upper Ypresian). Successively, the rotaliid diversity definitely declined, whereas other groups of larger foraminifera, and especially Alveolina and Nummulites, became more widespread and flourished with a large amount of species, up to the lower Bartonian SBZ17, when a final drop in rotaliid diversity is recorded. These major changes appear strictly linked to climate warming events such as Late Danian Event (LDE, generic diversification of rotaliids), Paleocene–Eocene Thermal Maximum (PETM, faunal turnover followed by abrupt decrease in both generic and specific diversity), Early Eocene Climatic Optimum (EECO, increase in number of K-strategists under oligotrophic conditions) and Middle Eocene Climatic Optimum (MECO, ultimate drop in diversity and competition with other larger foraminifera).