Although they originated around 180 million years ago, mammals underwent an adaptive radiation starting approximately 65 million years ago. Why?

• A. Mammals were not well adapted to the climate that existed before about 65 million years ago.
• B. Mammals were mostly nocturnal until 65 million years ago.
• C. Fur evolved in mammals around 65 million years ago, enabling them to withstand colder temperatures.
• D. All of the listed responses are correct.
• E. Between 180 and 65 million years ago, mammals were outcompeted by the well-established dinosaurs.