A

David

Darling

Oligocene

Oligocene

The Oligocene was the third geological epoch of the Cenozoic era. It occurred approximately 34–23 million yr ago. During the Oligocene epoch, the climate cooled. Many modern mammals evolved, including early elephants and Mesohippus, an ancestor of the modern horse. Only a few archaic mammals, such as titanotheres, survived into the epoch, and they became extinct before it ended.