Crocodiles are nasty critters. They're built like armored tanks; they eat almost anything -- including humans, pet dogs, footballs and diapers; and, if you haven't noticed, their skin is cracked and ugly. Now, scientists at the University of Geneva think they know why.
Lotion can't help this cracked skin.
Reptile skin is scaly. The spatial layout of the scales is largely controlled by genetics, although other positional factors can be involved. On the head of a snake, for instance, the scales overlap and are symmetrical on both sides of its face. If there are three shiny scales beneath one eye, you will find three shiny scales beneath the other eye.
But that's not true for crocodiles. While the scales on the rest of its body conform to a set of genetic rules in regard to layout, the scales on its head do not. Instead, they are non-overlapping, irregularly shaped, randomly positioned, and asymmetrical on both sides of its face. Why is a snake's face so aesthetically pleasing, while a crocodile's face looks like an old leather purse?
The authors believe that the positions of the head scales on a crocodile are largely determined by physical forces. As the underlying skeleton rapidly grows, the tough, keratinized skin of the crocodile cracks in response. Of course, genetics controls some of this (e.g., skull shape), but it also appears that randomness plays a big role in the placement of head scales.
And that's why crocodiles have a face that only a mother could love.
: Michel C. Milinkovitch, Liana Manukyan, Adrien Debry, Nicolas Di-Poï, Samuel Martin, Daljit Singh, Dominique Lambert, Matthias Zwicker. "Crocodile Head Scales Are Not Developmental Units But Emerge from Physical Cracking." Science
(Published Online November 29, 2012) DOI: 10.1126/science.1226265