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Crocodile head scales form by physical cracking

From: Ben Creisler

Another advance paper in Science that might be of interest:

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 (advance online publication)
DOI: 10.1126/science.1226265

Various lineages of amniotes display keratinized skin appendages
(feathers, hairs, and scales) that differentiate in the embryo from
genetically controlled developmental units whose spatial organization
is patterned by reaction-diffusion mechanisms (RDM). We show that
contrary to skin appendages in 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 distinct from RDM: 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