Unlike amphibians, mammals do not regenerate appendages. Except when they do. “If you amputate one of the branches off of the antler [of a reindeer], it will also regenerate,” Jeff Biernaskie told BioWorld. Even without amputation, the antlers of both male and female reindeer regenerate annually, including their skin. That regeneration is “the only large mammal model of true skin regeneration,” he said.