Eocene

noun

(Gr. eôs: dawn; kainos: new) Tertiary epoch which began at the end of the Palaeocene (56.5 million years ago) and ended at the beginning of the Oligocene (35.4 million years ago). It is noted for the expansion of mammalian stocks (horses, bats, and whales appeared during this epoch), and the local abundance of Nummulites (marine protozoans of the Foraminiferida). The Eocene Epoch is divided into the Ypresian, Lutetian, Bartonian, and Priabonian Ages.