A high level of genetic similarity have been found among North American cougar populations , suggesting they are all fairly recent descendants of a small ancestral group . Culver et al. propose the original North American population of P. concolor was extirpated during the Pleistocene extinctions some 10 @,@ 000 years ago , when other large mammals , such as Smilodon , also disappeared . North America was then repopulated by a group of South American cougars .