african broad-mouthed collagen creases endangered flat-mouthed folds gray grazer grey heavy herbivore herbivorous hide horns keratin large lattice structured mammal megafauna odd-toed ungulate perissodactyl placid powerful rhino rhinoceros skin snout southern white rhinoceros square-lipped rhinoceros strong thick threatened tough white rhinoceros wide-lipped rhinoceros wrinkled wrinkles eating feeding food mother Mud mud-covered muddy odd-toed-ungulate offspring southern-white-rhinoceros white-rhinoceros cow junior lattice-structured calf youngster