In other words, you do not believe in science.   The fact remains that humans living in North America is a relatively recent event, in comparison to the amount of time that humans have been on the earth.    

And it is a truly insignificant amount of time, compared to the time that countless species of other mammals have lived on on our continent.  In fact, North American had many truly natives species of mammals that were unique to our continent, and flourished here for many millions of years.