Paleocene

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It began 65.5 million years ago, and ended 55.8 million years ago.

The mammals started appearing 65.5 million years ago when the dinosaurs went extinct. They thrived because they didn't have any major predators like the dinosaurs to feed off of them. The mammals are still alive today, but they have evolved over time.

Mammals, such as whales, primates, and birds that were slowly evolving.