The period during which mammals dominated is called the Cenozoic Era, often referred to as the "Age of Mammals." This era began approximately 66 million years ago after the mass extinction event that wiped out the dinosaurs. The Cenozoic Era is characterized by the diversification and evolutionary success of mammals, birds, and flowering plants.
The Cenozoic Era is divided into two main periods:
- Paleogene Period
- Neogene Period
Thus, the correct answer is Cenozoic Era.