During the Cainozoic the continents moved into their present positions. The climate started warm, but cooling continued steadily. Finally ice ages occurred.
Previously, what is now the Cainozoic was divided into two periods, the Tertiary and the Quaternary. The Tertiary corresponded to the Palaeogene+Neogene. Now, the term 'Tertiary' is not used. Officially, it is 'deprecated'.
On land, the Cainozoic is the era of mammals, and of birds and flowering plants. Grassland became a major habitat. Aquatic mammals took over the roles of predatory reptiles like the mosasaurs and plesiosaurs. As a result, the ecological landscape of the Cainozoic has become quite different from the Mesozoic.
Images for kids
Cainozoic Facts for Kids. Kiddle Encyclopedia.