giant giant tortoise reptile shell tortoise aging endurable Galapagos tortoise heavy herbivore large leathery longevity old plodder plodding slow and steady tough wisdom wise animal Galapagos Island national park slow turtle walking woods abstract age aged appearance armor armored armorment armour armoured armourment astrochelys-radiata carapace critically-endangered endangered hide large tortoise Madagascar plod protection protective radiated-tortoise reptilian size skin strength strong texture textured textures zoo aldabra giant tortoise aldabrachelys gigantea eating eating grass elongated neck neck Seychelles