Oligocene

The Oligocene is a geologic epoch of the Paleogene Period, lasting from about 33.9 to 23.0 million years ago. It follows the Eocene and precedes the Miocene. The name derives from Greek words meaning “few fossils of the recent type,” reflecting early observers’ impressions of the rocks. In the standard timescale, the epoch is divided into the early Rupelian (roughly 33.9–28.1 Ma) and the late Chattian (roughly 28.1–23.0 Ma).

During the Oligocene, Earth underwent significant global cooling that continued the trend from the warmer Eocene. Polar ice sheets began to expand, sea levels fluctuated, and climate became more seasonal and arid in many regions. These changes contributed to the widespread development of open habitats, including more extensive grasslands in some areas, and influenced patterns of ocean circulation and biogeography.

The epoch saw notable evolution and diversification among mammals and other groups. Mammalian faunas diversified with continued evolution of hoofed mammals (perissodactyls and artiodactyls), as well as rodents and early primates. The first true catarrhine primates appear toward the end of the Oligocene, and many modern mammalian orders continued to solidify their basic forms in this interval. Floral communities also shifted, with a trend toward more modern-dominated assemblages in many regions.

The Oligocene played a key role in setting the stage for the Miocene, influencing continental configurations, climate patterns, and the distribution of plants and animals. Its rocks and fossils are widely studied to understand late Paleogene environments and the early evolution of many modern lineages.