What is the closest related species to humans native to the US?

Humans evolved in Africa, and primates evolved originally in Asia. Asia has had a long history of exchanging faunal species with Europe, Africa and North America. Since there is no living species of primate native to the USA, we have to go back in evolutionary history to a time before the evolution of the first primate to find that closest relative.

Unfortunately, the evolutionary relationships among mammalian orders is not well resolved, but the picture is clearer than in the early 1990s owing to the wider availability of molecular data. Using molecular data, we are pretty certain that primates are most closely related to the colugo and the tree shrews, but neither of these are native to the USA. Currently, many scientists subscribe to the view that the next closest relatives of humans are lagomorphs (rabbits and hares) and rodents and that they are each other's closest relatives. There is however a huge problem with that relationship. That is because rodents and lagomorphs have testicles that are drastically different in position, so drastically different that their common ancestor must have no external testicles. That means that common ancestor goes way back in time and therefore is not as recent as the molecular data has been interpreted to show. That means the current view that rodents and lagomorphs are the closest relatives of primates, the colugo and tree shrews is problematic.

Rather than embracing a problematic theory, I prefer to be more conservative and instead prefer to pick a mammal that is perhaps not the absolute closest relative to us, but is still pretty close. That relative is the shrew. It is native to the United States, and its ancestors originated in Asia, and the shrew-like mammals are in turn ancestors to the Boreoeutheria, to which humans, lagomorphs, colugo, tree shews, bats carnivores, whales and ungulates belong. That also means that we have quite a few relatives native to the USA that are close relatives of humans, and these include bears, weasels, squirrels, mice, rats, wolves, raccoon, cougars, otters, seals, sea lions, deer, goat, sheep, bison, bats, rabbits, hares, shrews, moles, and the extinct American horses and camels. Perhaps, with more data in the future, we can figure out mammalian relationships better. For now, I am rejecting the close relationship between rodents and lagomorphs on morphological grounds, and therefore I also reject the hypothesis that rodents and lagomorphs are more closely related to primates, colugos and tree shrews than other boreoeutherian mammals.

Being an atheist implies no special knowledge or expertise in science in general or biology in particular. For example, all Buddhists are atheists because they follow the teachings of a man rather than worship a god - would you ask the same question to any random Buddhist?

Atheist: a person who doesn't ascribe perfectly natural events to the influence of a fictitious supernatural being who loves you so much that he'll roast you for all eternity if you happen to believe in the wrong version of his non-existent self