Mammals. Brontotherium, Indricotherium, Enteledont, Hyaenodon, and Mesohippus are found.
Reptiles. Reptiles were abundant in the Oligocene. Choristodera, a group of semi-aquatic, crocodile-like, diapsid (archosauromorph?) reptiles that had originated in the Jurassic, possibly as far back as Late Triassic, became extinct early in the Oligocene, possibly due to climate changes. Snakes and lizards did diversify to a degree.
Sea life. The Oligocene oceans had some resemblance with today's fauna. Bivalves were present. The baleen and toothed cetaceans (whales) had just appeared, and their ancestors, the Archaeocet cetaceans, remained relatively common, although their were falling as the Oligocene progressed, possibly due to climate changes and competition with today's modern cetaceans and the Charcharinid sharks, who also appeared in this epoch. Pinnipeds (marine mammals such as seals, walruses, and sea lions) probably appeared near the end of the epoch from a bear-like or otter-like ancestor.
- Geologic time scale
- Haines, T. 1999. Walking with Beasts: A Prehistoric Safari. New York: Dorling Kindersley Publishing, Inc. ISBN 0563384492.
- Mayr, E. 2001. What Evolution Is. New York: Basic Books. ISBN 0465044255
- Ogg, J. 2004. Overview of Global Boundary Stratotype Sections and Points (GSSP's). Retrieved June 22, 2007.
All links retrieved December 19, 2018.
- PaleoMap Project: Oligocene at Climate History by Christopher R. Scotese