armor armored armorment armour armoured armourment Australian-freshwater-crocodile backstraps bony-ridges crocodile crocodylus-johnsoni danger dorsal-surface exotic fauna fresh-water-crocodile freshie hide Johnstone's-crocodile leather leathery lethargic omnivorous opportunistic opportunistic-predator osteoderms patterns powerful predator reptile reptilian ridges rough rugged scales scutes semi-submerged skin tail tail-scutes territorial texture textured textures