Foraminifera are separated into two groups following their life strategy, namely the planktonic and the benthic foraminifera. Planktonic foraminifera occur worldwide over broad laditudinal and temperature belts. They typically float in the surface or near-surface waters of the open ocean.  Their wide geographical range, combined with a short vertical stratigraphic time range (due to rapid evolution), make them excellent index fossils at family, generic and species levels. The figure on the left shows the ecological distribution of larger benthic foraminifera and key smaller benthic and planktonic foraminifera through space and time.