designating or of the second geologic epoch of the Paleogene, characterized by a warm climate and the development of mammals
See Eocene in American Heritage Dictionary 4
(ēˈə-sēnˌ)
adjective
Of or belonging to the geologic time, rock series, or sedimentary deposits of the second epoch of the Tertiary Period, characterized by warm climates and the rise of most modern mammalian families. See Table at geologic time.