On Old Earth, the third epoch of the Tertiary period and Cenozoic era, lasting from 34 to 23 million years ago.
The Oligocene was intermediate in many ways between the preceding Eocene, with its extensive tropical forests, and the following savannas of the Miocene. The largest land mammal ever, Indricotherium, lived during this time in Asia.
Elsewhere in the galaxy, the Muuh discovered the ancestral species of the Soft Ones in the Perseus Arm during this time and began provolution work. The Tunnlers created an extensive wormhole network that reached both the Sagittarius and Orion Arms.