Spines on seashells, which offer protection from the crushing jaws of potential predators, are often cited as an example of similar features that have evolved independently in different species. Now, their shape can be explained by the physics of shell formation.

Derek Moulton at the University of Oxford, UK, and his colleagues modelled the interactions between the hard edge of the shell and the mollusc mantle that secretes new shell material during growth. Variations in growth rates and the stiffness of new shell could account for the diversity of spine shapes found on the shells of different species in sea-snail families such as Muricidae.

A mechanical model could explain the similarities in shell spines seen across various species, the authors suggest.

Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1220443110 (2013)