The Cenozoic Era spans only about 65 million years, from the end of the Cretaceous Period (Mesozoic Era), and the extinction of non-avian dinosaurs, to the present. The Cenozoic is sometimes called the Age of Mammals, because the largest animals found on land during this time have been mammals. This is a misnomer for several reasons. First, the history of mammals began long before the Cenozoic Era began. Second, the diversity of life during the Cenozoic is far wider than mammals. The Cenozoic could also be called the "Age of Insects," "Age of Teleost Fish," "Age of Birds," or the "Age of Flowering Plants" just as accurately.
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The Cenozoic Era is divided into two main sub-divisions: the Tertiary and the Quaternary. Most of the Cenozoic is the Tertiary, from 65 million years ago to approximately 1.8 million years ago. The Quaternary includes only the last 1.8 million years. |