designating or of the first geologic epoch of the Paleogene, characterized by lower sea levels, the development of modern mountain ranges, and the development of flowering plants, birds, and mammals
paleo- + -cene
See Paleocene in American Heritage Dictionary 4
Of or belonging to the geologic time, rock series, or sedimentary deposits of the first epoch of the Tertiary Period, marked by the appearance of placental mammals and continental collisions leading to the formation of the Rocky Mountains and the Himalayas. See Table at geologic time.