SHELLS AND MARINE REVOLUTIONS: EXPERIMENTAL TESTS OF THEORETICAL SHELL SHAPES

The increasing availability of 3D printing has opened a host of new experiments for paleontologists. We used this technology to evaluate the strength of several theoretical gastropod shells subjected to durophagous predation. While the mathematics of shell shape has been described in the past, the adaptive value and functionality of different shapes is still largely unknown. It has been hypothesized that some shells provide less protection against crushing predators than others due to their geometry, but shape has yet to be tested in isolation. Durophagous predation presents a unique challenge because successful attacks leave little identifiable evidence in the fossil record. Investigators using only fossils must rely on repair scars from failed attacks, the frequency of which may not accurately represent predation intensity. We conducted compression tests to examine whether shell shapes have evolved as one would expect in a scenario of escalation in which mollusks adapted to durophagous predation alone. Using 3D printing, we removed disparities in material properties to analyze shape exclusively, allowing us to compare geometries in a controlled system. We tested planispiral, open coiling, and umbilicate shells as well as more tightly coiled forms and found that some differences in shell strength could be attributed to geometry. Our analysis experimentally addresses whether more complex shapes, as emergent during the Mesozoic Marine Revolution (MMR), are more resistant to durophagous predation. Thus, we can erect a testable hypothesis that observed changes in occurrence of resistant shell shapes presents a direct, measurable response to changes in durophagous predation pressure, such as the increase in shell-crushing fishes during the MMR.