The New World rats and mice are a group of rodents from the family Cricetidae. They are mammals with fur and long tails. These animals live in the wild in North and South America. The group is very large, with about 500 different species. Biologists are not sure whether the group is descended from a common ancestor, so there is no scientific name for it. There are three subfamilies, Neotominae, Sigmodontinae and Tylomyinae.