animal domesticated farm fetlock foot hoof hooves horse keratin leg mammal tread walk african broad-mouthed collagen endangered flat-mouthed gray grazer grey heavy herbivore herbivorous hide horns large lattice structured megafauna odd-toed ungulate perissodactyl placid powerful rhino rhinoceros skin snout southern white rhinoceros square-lipped rhinoceros strong thick threatened tough wide-lipped rhinoceros creases folds white rhinoceros wrinkled wrinkles cow eating food junior lattice-structured mother odd-toed-ungulate offspring southern-white-rhinoceros