It had long been assumed that dire wolves made themselves at home in North America before gray wolves followed them across the Bering Land Bridge from Eurasia. For decades, paleontologists have remarked on how similar the bones of dire wolves and gray wolves are. Dire wolves, it now appeared, had evolved in the Americas and had no close kinship with the gray wolves from Eurasia; the last time gray wolves and dire wolves shared a common ancestor was about 5.7 million years ago. Perri, Mitchell and their colleagues found no DNA evidence of interbreeding between dire wolves and gray wolves or coyotes. Dire wolves were genetically isolated from other canids, Mitchell notes, so “hybridization couldn’t provide a way out” because dire wolves were probably unable to produce viable offspring with the recently arrived wolves from Eurasia.