Reaction-diffusion processes: Application to the morphogenesis of ammonoid ornamentation

Ammonoid ribs, tubercles, keels and other ornamental features are organized in a great diversity of patterns. From the viewpoint of developmental biology, these patterns can only be understood as the product of a dynamical system controlled by genes but also dependent upon biochemical and mechanical processes. Here, an attempt is made to view the development of ammonoid ornamentation in the light of reaction-diffusion systems, though it is emphasized that diffusion of biochemical morphogens is only one of several possible interpretations of this class of theoretical models. Also, morphogenetical gradients and threshold functions are presented as partial explanations for some specific ornamental patterns.