The Tertiary Period is known as "The Age of Mammals." It is divided into five epochs: the Paleocene Epoch, the Eocene Epoch, the Oligocene Epoch, the Miocene Epoch and the Pliocene Epoch. It marks the start of the Cenozoic Era and started 65 million years ago. The Tertiary Period lasted 63 million years and ended with an Ice Age. It is preceded by the Cretaceous Period and followed by the Quaternary Period.
Each epoch of the Tertiary Period is defined by its climate, geography and animal life.
The first hominids, ancestors of humans, appeared in the Pliocene Epoch. Rhinos, camels, horses and ape-like primates appeared in the Miocene Epoch. Dogs, cats, pigs and toothed whales appeared in the Oligocene Epoch. Bats and ancestors of elephants appeared in the Eocene Epoch. Rodents and the first primates appeared in the Paleocene Epoch.
Plant life during the Tertiary Period is similar to the plant life on Earth today and included woodlands and grasslands. The grasses supported herd animals that appeared after the extinction of the dinosaurs in the Cretaceous Period. With the dinosaur extinction event, mammals diversified and grew in size and numbers, hence the name "The Age of Mammals." for the period. Fish, birds and insects also diversified during the Tertiary Period.
The climate cooled near the end of the Tertiary Period, causing glaciers to form at the poles. Great amounts of the oceans and seas became ice bridges large enough for herds of animals and plants to migrate from one continent to another: from Asia to North America, Great Britain to Europe and South East Asia to Borneo.