Cenozoic Era
Paleogene Period
66–23 Million Years Ago
The Paleogene followed the K–Pg extinction and witnessed the explosive diversification of mammals. With dinosaurs gone, mammals rapidly evolved to fill empty ecological niches — from tiny insectivores to the first whales, early horses, and primates. The Eocene was particularly warm, but a long-term cooling trend began that would eventually lead to the ice ages.
Environment
Climate & Environment
The Paleocene–Eocene Thermal Maximum was one of the warmest intervals in the Cenozoic. Gradual cooling followed, culminating in Antarctic glaciation by the end of the Eocene.
Fauna & Flora
Signature Life Forms
Early primates (Adapidae, Omomyidae)
First whales (Ambulocetus, Basilosaurus)
Giant flightless birds (Gastornis)
Diversification of modern mammal orders
