E·o·cene a. Geol. Pertaining to the first in time of the three subdivisions into which the Tertiary formation is divided by geologists, and alluding to the approximation in its life to that of the present era; as, Eocene deposits. -- n. The Eocene formation.
n : from 58 million to 40 million years ago; presence of modern
mammals [syn: Eocene epoch]