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 • Basic Overview
The Age of Mammals
The Mesozoic Era, the age of the dinosaurs, had come to a dramatic end. Mass extinction had devastated life on Earth. All dinosaurs except birds had disappeared. The Mesozoic Era had ended, and the Cenozoic Era—the age of mammals—had begun.
Tropical climates supported species diversity.
 Fifty million years ago during the first part of the Cenozoic Era (the Tertiary Period) warm climates reached from pole to pole. These tropical habitats were home to a diversity of fishes, birds, insects, and plants. Many resembled species that live today. During this period, mammals began to develop new features and reach new sizes.
Changing climates affected mammal diversity.
On an ever-changing Earth, temperatures began to fall again after the first five million years of the Cenozoic Era, and grasslands spread, transforming the landscape. As the planet changed, mammals changed, some going extinct, new ones always evolving.
Continue to Fossil Lake and Tropical Forests. >>
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