The mass-extinction event at the Cretaceous/Tertiary boundary (C/T in text; K-T on figures) exterminated all but one species of the planktonic Foraminifera (Guembelitria cretacea Cushman). Although not all details have been clarified yet, all Paleocene planktonic Foraminifera may have evolved from this sole survivor. Globigerina minutula Luterbacher and Premoli Silva is the first true Paleocene species to appear; it develops into Globigerina fringa Subbotina, and later on probably into Globigerina eugubina Luterbacher and Premoli Silva. Essentially, the stratigraphy of several complete sections shows a similar pattern: abrupt extinction of plankton followed by deposition of a thin lamina with high...