We show today in the journal Science that face and jaws scales of crocodiles are not developmental units but emerge from a physical process analogous to cracking.
Mammals, birds, and reptiles exhibit keratinized skin appendages (hairs, feathers and scales) that differentiate in the embryo from genetically controlled developmental units. We show that contrary to skin appendages in all other amniotes (as well as body scales in crocodiles), face and jaws scales of crocodiles are random polygonal domains of highly keratinized skin, rather than genetically controlled elements, and emerge from a physical self-organizing stochastic process: cracking of the developing skin in a stress field. We suggest that the rapid growth of the crocodile embryonic facial and jaw skeleton, combined with the development of a very keratinized skin, generates the mechanical stress that causes cracking.
More info is available on the ‘croc crack’ page.