Answer: oligocene

AnswerCrossword Clue
OLIGOCENEEpoch of the Tertiary Period
OLIGOCENEEpoch after the Eocene
oligocenebelonging to a certain geological time period
oligoceneOf, relating to, or denoting the third epoch of the Tertiary period, between the Eocene and Miocene epochs
oligoceneThe Oligocene epoch or the system of rocks deposited during it