The
International Commission on Stratigraphy (ICS) has assigned the extinction of
Discoaster brouweri as the
defining biological marker for the start of the
Calabrian Stage of the
Pleistocene, 1.806 million years ago. ICS has assigned the extinction of
Discoaster pentaradiatus and
Discoaster surculus as the defining biological marker for the start of the
Gelasian Stage, 2.588 million years ago, the earliest stage of the
Pleistocene. ICS further assigned the extinction of
Discoaster kugleri as biological marker for the start of the
Tortonian Stage of the
Miocene, 11.62 million years ago. == Species ==