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