EXPLORING THE FUNCTION OF SUTURE COMPLEXITY WITH EXPERIMENTAL COMPRESSION OF 3D PRINTED AMMONOIDS

The unique patterns of sutures preserved in ammonoid fossils have fascinated scientists, mathematicians, and the general public for years and have been used to define both major clades and time intervals. These sutures mark where the outer shell walls joined the inner walls that created air-filled chambers. Many hypotheses have been proposed to explain possible functions of increasingly complex sutures and septa over time, but few have been experimentally tested. We have directly tested the long-held hypothesis that the complex shapes of septa provided increased protection against crushing predators. This experiment used 3D printing technology to conduct physical compression tests on septal walls. CT scans of fossil ammonoids with well-preserved suture types were used to 3D print models, using a brittle material. These were crushed using flat plates on an Instron to represent a crushing durophagous vertebrate predator. Peak load sustained by different septa were used to infer the adaptive value of their shapes against shell-crushing attacks. Our experimental results reveal new insights to help paleoecologists move forward in settling the long-running debate about the function of suture evolution. This experiment further explores combining ancient morphologies with current 3D printing technology.