The Cenozoic Era, which is the term we use to refer to the current Era, began 66 million years ago. This particular period of time involves some critical processes that have molded the fauna and flora how I know it today, in the sense that is in this era, where toke place one of the major fauna migration on the American continent, which consisted in the displacement of animals between the North part of the continent with the South part. So the answer to this question is C. 66 million years ago.
