1. A geological epoch of the Paleogene Period, lasting from approximately 34 to 23 million years ago, characterized by cooling climate and the expansion of grasslands.
Usage: geology; capitalized; often used with the definite article 'the'

1. Of, relating to, or denoting the Oligocene epoch or rocks and fossils from that time period.
Usage: geology; capitalized

Examples

• The Oligocene epoch saw the development of the first true grasses.
• Oligocene fossils reveal the presence of early primates and carnivores.
• During the Oligocene, global temperatures declined significantly.
• Oligocene rocks in this region contain abundant marine deposits.
• Many modern mammal families first appeared during the Oligocene.
• The Oligocene followed the Eocene and preceded the Miocene.