Reindeer and caribou are two names for the same genus and species, Rangifer tarandus. In Europe, they are called reindeer, and the wild populations in North America are called caribou. In comparison to body size, reindeer have the largest and heaviest antlers of all living deer species. Both males and females grow antlers. A male’s antlers can measure up to 51 inches, and a female’s antlers can reach 20 inches. Unlike horns, antlers fall off and grow back larger every year. As new antlers grow, the reindeer is said to be “in velvet,” because skin, blood vessels, and soft fur cover the developing antlers. When the velvet dries up, the reindeer rubs it off against rocks or trees, revealing the hardened, bony core.