abstract age aged appearance armor armored armorment armour armoured armourment astrochelys-radiata carapace critically-endangered endangered giant tortoise herbivore hide large tortoise leathery longevity Madagascar old plod plodding protection protective radiated-tortoise reptile reptilian shell size skin slow strength strong texture textured textures tortoise zoo rough scaly tough eating feeding giant-tortoise large-tortoise pattern patterned leaves meal Camouflage light mixed-light patchy shade shadows sunlight sunshine