How the Crocodile Got Its Scales

Mammalian hairs, avian feathers, and reptile scales differentiate and grow from genetically controlled units. Using three-dimensional (3D) computer graphics and computational biology to study scale generation, Milinkovitch et al. (p. 78 , published online 29 November; see the cover) show that crocodilians' face and jaw scales do not follow this rule but emerge by physical cracking of the developing skin in a tension field. Thus, a crocodile's head scales are not genetically controlled developmental units but are random polygonal domains of keratinized skin that are generated from a self-organizing physical process.