CFD Time Machine: Using CFD to Understand the History of Long Extinct Swimmers

Ammonoids are a group of cephalopods that were found in oceans worldwide for nearly 300 million years. These organisms once swam freely in the ocean and were as abundant as fish are today but went extinct 65 million years ago in the same extinction that killed the dinosaurs. In this study, we use Computational Fluid Dynamics model (Ansys V18.0) to study the locomotion of these now extinct animals. The fossil record shows that ammonoids underwent numerous periods of evolutionary boom and bust. During these cycles, ammonoids with a planispiral shell type often show clear shifts in their shell morphology, strongly emphasizing traits such as lowered cross-sectional area or increased coiling exposure. However, because there are no modern members of the group and there is no soft tissue preservation, it has been difficult for researchers to understand the implications of these shifts on their swimming pattern. We used CFD to study the hydrodynamic impacts of their morphological transformation, in terms of drag and lift. Incremental changes in shell shape across three common shape characters were studied: Shell inflation (total shell width), Whorl Expansion (the rate at which coil diameter increases, and Umbilical Exposure (the ratio of exposed coiling to total diameter). Our results show that drag and lift are sensitive not only to the particular parameter being changed but also that they are non-uniformly sensitive to the direction (increasing or decreasing) and magnitude of how that parameter is being changed.