The development of ammonoid septa: An epithelial invagination process controlled by morphogens?
Titel:
The development of ammonoid septa: An epithelial invagination process controlled by morphogens?
Auteur:
Hammer, Øyvind
Verschenen in:
Historical biology
Paginering:
Jaargang 13 (1999) nr. 2-3 pagina's 153-171
Jaar:
1999
Inhoud:
Suture lines are important in ammonoid taxonomy. Their complex morphologies, caused by iterated invaginations of the posterior body wall, can be explained using a mechano-chemical model inspired by modem developmental models for epithelial folding in kidneys, lungs, teeth, mammary glands and other organs. A morphogen, organized to form a regular spacing pattern by reaction-diffusion dynamics or similar processes, induces changes in cell shape and/or rate of proliferation, causing invagination and the formation of lobes. Interactions between mechanical and chemical effects, combined with expanding size due to overall growth, produce a “fractal”; pattern of smaller (secondary) invaginations superimposed on larger (primary) ones. The pattern of increasing sutural complexity that is observed in ammonoid evolution may be a simple heterochronic effect, that allowed iterated invagination to be extended to higher and higher levels of folding. In contrast with some earlier theories, the present model is based on the view that the development of ammonoid septa must have been under relatively strict genetic control.
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