DWARFING AND EXTINCTION IN EOCENE AND OLIGOCENE PLANKTONIC FORAMINIFERA

Dwarfing has commonly been associated with extinction events in planktonic foraminifera. Examples of dwarfing in planktonic foraminifera through the Eocene and Oligocene are species specific and do not appear to affect the entire assemblage. In many cases the smaller forms (dwarfs) survive for thousands to millions of years following the extinction of their larger counterparts. In examining the interval from the latest middle Eocene through upper Oligocene (38 – 27 Ma) a marked decrease in size is associated with the extinction of Acarinina mcgowrani, Globigerinatheka index, Subbotina linaperta, Pseudohastigerina micra, Turborotalia ampliapertura, and Paragloborotalia opima. Multispecies stable isotope analysis reveals that the extinction of Acarinina mcgowrani (38 Ma) was not associated change in sea surface temperature. Mechanisms in the extinction and dwarfing of this species may have been related to enhanced eutrophication and deterioration of algal symbiotic associations.