Foraminifera have a geological range from the earliest Cambrian to the present day.  Forams with hard tests were not common until the Devonian with the introduction of fusulinids into the fossil record, which later died out at the end of the Palaeozoic.  The earliest forams were all benthic forams; planktonic forms do not appear in the fossil record until the Mid-Jurassic.  Warm temperatures "greenhouse conditions" during the Cretaceous helped the diversification of the planktonic foraminifera.  An evolutionary burst occurred during the Paleocene (globigerinids) and Eocene (nummulites).  Numbers of species of large foraminifera began to decline in the Miocene and diversity of planktonic forams has also decreased since the end of the Cretaceous.