The Cenozoic Era is the Age of which organisms?

• A. Dinosaurs
• B. Reptiles
• C. Mammals
• D. Plants

Answer: (C)

The main idea here is that the Cenozoic is defined by the rapid rise and diversification of mammals after the end of the age of dinosaurs. When non-avian dinosaurs went extinct near the end of the Mesozoic, mammals—ranging from small placentals to the large megafauna that roamed later in the era—expanded into many ecological roles that dinosaurs previously occupied. This radiation laid down the broad spectrum of mammal lineages and forms we see today, including the eventual appearance of humans. While reptiles, birds, and plants were and are part of Earth’s ecosystems, it’s the widespread diversification and dominance of mammals that characterizes the Cenozoic, earning it the title often described as the Age of Mammals.