The answer is C. Cenozoic era. It's the era when mammals evolved into larger organisms and began subdividing into various species. Cenozoic is also known as the age of mammals, because it's the mammals that mostly occupied the lands.
There are so many examples for that in different areas, like TPT1 experiment carried out in our lab recently.Here's one link: http://www.alfa-chemistry.com/tpt1-cas-167218-46-4-item-290583.htm
