Stability–Maneuverability Tradeoffs Provided Diverse Functional Opportunities to Shelled Cephalopods

Abstract

Stability-maneuverability tradeoffs impose various constraints on aquatic locomotion. The fossil record houses a massive morphological dataset that documents how organisms have encountered these tradeoffs in an evolutionary framework. Externally shelled cephalopods (e.g., ammonoids and nautiloids) are excellent targets to study physical tradeoffs because they experimented with numerous conch morphologies during their long-lived evolutionary history (around 0.5 billion years). The tradeoff between hydrostatic stability and maneuverability was investigated with neutrally buoyant biomimetic models, engineered to have the same mass distributions computed for their once-living counterparts. Monitoring rocking behavior with 3D motion tracking reveals how stability influenced the life habits of these animals. Cephalopods with short body chambers and rapid whorl expansion (oxycones) more quickly attenuate rocking, while cephalopods with long body chambers (serpenticones and sphaerocones) had improved pitch maneuverability. Disparate conch morphologies presented broad functional opportunities to these animals, imposing several advantages and consequences across the morphospace. These animals navigated inescapable physical constraints enforced by conch geometry, illuminating key relationships between functional diversity and morphological disparity in aquatic ecosystems. Our modeling techniques correct for differences in material properties between physical models and those inferred for their living counterparts. This approach provides engineering solutions to the obstacles created by buoyancy, mass distributions, and moments of inertia, permitting more lifelike, free-swimming biomechanical models and aquatic robots.

The Hydrodynamics of Ammonoid Swimming: Equations of Motion and Rocking Resonances

“…The presence of ribs and other ornamentations will also affect circular drag in real ammonoids. In the case of multiple jet pulses, the "build-up" of horizontal speed shown in Figure 2 replicates a similar pattern observed with experimental 3D models well [18,32]. Thus, even considering the differences between the analogic and numerical models, the theoretical data calculated here are in good agreement with those measured for several consecutive pulses, which indicates that the modelling may be a good starting point for future calculations with more complex conch shapes.…”

“…Fossils 2023, 1, FOR PEER REVIEW 6 els well [18,32]. Thus, even considering the differences between the analogic and numerical models, the theoretical data calculated here are in good agreement with those measured for several consecutive pulses, which indicates that the modelling may be a good starting point for future calculations with more complex conch shapes.…”

“…These results compare well with measurements from analogic 3D models of ammonoids propelled by an internal funnelling mechanism. Petermann and Ritterbush [18,32] present data for the horizontal velocity (their Figure 6A) and angular velocity (their Figure 8B of ref. [18]) for a 3D serpenticone model with geometrical characteristics and size similar to those used here.…”

Investigations into 3D-printed nautiloid-inspired pressure housings

“…Fused deposition modeling (FDM) can print morphologically accurate 3D shells for certain practical tests of performance, such as the righting moment of cephalopod shells and their fluid retention as a function of septal complexity [18,[25][26][27]. One conclusion drawn from this kind of experimentation was that the fluid retention from complex, folded septa in ammonoids would have allowed better control over buoyancy compared to extant nautilids.…”