african broad-mouthed calf collagen cow creases endangered flat-mouthed folds gray grazer grey heavy herbivore herbivorous hide horns junior keratin large lattice-structured mammal megafauna mother odd-toed-ungulate offspring perissodactyl placid powerful rhino rhinoceros skin snout southern-white-rhinoceros square-lipped rhinoceros strong thick threatened tough white rhinoceros wide-lipped rhinoceros wrinkled wrinkles youngster close close-up eye eye-lashes eye-lid eating feeding food Mud mud-covered muddy white-rhinoceros alert biological-interaction bird black curious inquisitive Myna myna-birds mynah Noisy plumage precocious square-lipped-rhinoceros symbiosis symbiotic watchful wide-lipped-rhinoceros black-rhinoceros critically-endangered Diceros bicornis herbivorous-browser hook-lipped-rhinoceros surface texture textures zoo