of, denoting, or formed in the third epoch of the Tertiary period, which lasted for 10 000 000 years
noun
2. the Oligocene
Word origin
C19: oligo- + -cene
Oligocene in American English
(ˈɑlɪgoʊˌsin)
adjective
[sometimeso-]
designating or of the third and last geologic epoch of the Paleogene, characterized by cold climate, the formation of vast grasslands, and the further development of mammals