25 million years – 25 metres
Open grasslands are common. There are plenty of sabre-toothed carnivores around. Flowering plants evolve and speciate.
Image: Eusmilus, a false saber tooth cat, hunting Palaeotherium, a smallish related animal. Deagostini | UIG | Science photo library
Oligocene epoch 34-23 million years ago represents an important transition. Climate was cooling and glaciers at Antarctica were frozen and melted again. Climate was, however, still warmer than today. Also flora and fauna had major changes in relatively short time. Tropical forests regressed and graslands expanded. At the open landscape the size of animals grew and ability to run improved as exemplified by the horse family. During the epoch also cat family and old world monkeys appeared. The rodents diversified and replaced the ancient multituberculates that had lived already at the time of dinosaurs.
Oligocene is the last epoch of the warm Paleogene period. 23 million years ago begins Neogene period that represents transition toward our current flora, fauna and icehouse climate.