The wolf is the most specialized member of the genus Canis in the direction of cooperative big game hunting, as demonstrated by its morphological adaptations to tackling large prey, its more gregarious nature, and its highly advanced expressive behavior. It is nonetheless closely related enough to smaller Canis species, such as the coyote and golden jackal, to produce fertile hybrids. It is the only species of Canis to have a range encompassing both Eurasia and North America, and originated in Eurasia during the Pleistocene, colonizing North America on at least three separate occasions during the Rancholabrean. It is a social animal, travelling in nuclear families consisting of a mated pair, accompanied by the pair's adult offspring. The wolf is typically an apex predator throughout its range. It feeds primarily on large wild ungulates, though it also eats smaller animals, livestock, carrion, and garbage. A seven-year-old wolf is considered to be relatively old, and the maximum lifespan is about 16 years.