Contrary to popular belief crocodiles don't have scales on their heads. They are just cracks in the thick skin on their skulls. The rest of the body does have scales. How the animal develops biologically is interesting. Each scale forms from a discrete scale primordium. For example, scales at similar points each side of the body are identical.
The deep lines on the head are unique to each crocodile, like a fingerprint. Indeed, the lines are not symmetrical. Now it is possible to identify young crocodiles without tagging, to follow their growth.
Having no primordia on a crocodile's head is functional. Mounds of skin build up and form an active memrocobrane. Receptors detect fine vibrations in water. This helps in hunting.
It has been hypothesised that fingerprints form in the same way as the "cracks" on the heads of crocodiles. This unregulated gene formation building on earlier skin development is probably the reason why identical twins have different fingerprints. The final shape of all creatures was believed to be totally preprogrammed by genes.