WANG, G; WARD, P; DANIEL, T; Univ. of Washington: The whorl is greater than the sum of its parameters: A finite element analysis of gastropod shell coiling

The fossil record is replete with different gastropod shell morphologies. This extensive paleontological record has contributed a great deal to the understanding of the mode and tempo of evolution. Although much is known about the distribution of morphological forms in the fossil record, there has been relatively little quantitative study of the functional significance of these forms and the selection pressures that lead to the diversity of shell morphology. We tested the hypothesis that the evolution of the helically coiled shell in gastropods is an adaptive response to predation pressure by increasing shell strength. To determine the biomechanical consequence of increasing shell coiling, we built finite element models with increasing shell heights and degrees of axial coiling and subjected these models to virtual inward forces at the perimeter of the aperture. The inward forces offer a simplified model for the biting forces of a larger predator, and cause mechanical stresses in the shell. Equivalent Cauchy stress is a measure of these concentrations of forces in a structure, and the maximum equivalent Cauchy stress is indicative of the strength of a structure. We investigated how stresses vary with increasing helicity due to changing spire height and axial curvature. Our results show that stresses are decreased with increased spire height, and with increased shell curvature. We also investigated how stresses vary when spire height and axial curvature vary simultaneously. Our data also show that the contributions of individual parameters changes to lowering stress do not linearly sum to the stresses in shells where both parameters are varied simultaneously.