Assessing the Morphological Impacts of Ammonoid Shell Shape through Systematic Shape Variation

Abstract

A substantial body of research has been accumulated around ammonoids over several decades. A core aspect of this research has been attempts to infer their life mode from analysis of the morphology of their shells and the drag they incur as that shell is pushed through the water. Tools such as Westermann Morphospace have been developed to investigate and scaffold hypotheses about the results of these investigations. We use Computational Fluid Dynamics (CFD) to simulate fluid flow around a suite of 24 theoretical ammonoid morphologies to interrogate systematic variations within this space. Our findings uphold some of the long-standing expectations of drag behavior; conch inflation has the greatest influence over ammonoid drag. However, we also find that other long-standing assumptions, such as oxyconic ammonoids being the best swimmers, are subject to substantial variation and nuance resulting from their morphology that is not accounted for through simple drag assessment.

Resurrecting extinct cephalopods with biomimetic robots to explore hydrodynamic stability, maneuverability, and physical constraints on life habits

“…Each of these shapes would have had hydrodynamic consequences 13 , 23 , 33 , modifying the physical properties of the fundamental conch shape. Furthermore, the hydrodynamic properties of particular shapes, in terms of directional swimming and maneuvers, are dependent upon size 13 , 19 . Ectocochleates had to navigate changing physical properties throughout ontogeny, while responding to various physical tradeoffs.…”

“…These morphologies are generally interpreted as nekton 24 , capable of reaching higher swimming speeds. In contrast, inflated forms (i.e., sphaerocones) incur higher hydrodynamic drag in turbulent flow, yet may be more efficient at smaller scales and/or velocities (i.e., lower Reynolds numbers 13 , 19 , 20 , 32 ). Recent computer simulations demonstrate that serpenticones (forms exposing their earlier whorls) do not incur much more drag than oxycones, despite their complex flank topologies 20 .…”

Stability–Maneuverability Tradeoffs Provided Diverse Functional Opportunities to Shelled Cephalopods

“…A conch's external shape constrains how the living animal interacts with surrounding water during locomotion (i.e., drag, lift, etc. ; Trueman 1940 ; Denton 1974 ; Chamberlain 1976 , 1981 , 1993 ; Jacobs 1992 ; Jacobs et al 1994 ; Jacobs and Chamberlain 1996 ; Naglik, Tajika, et al 2015 ; Hebdon et al 2020 , 2021 ; Peterman, Hebdon et al 2020 ; Peterman, Shell et al 2020 ; Hebdon, Ritterbush et al 2022 ), while internal morphology and coiling parameters influence hydrostatics (i.e., buoyancy, stability, directional efficiency of movement; Fig. 1C ; Saunders and Shapiro 1986 ; Hoffmann et al 2015 ; Peterman, Barton et al 2019 ; Peterman, Mikami et al 2020 ; Peterman, Yacobucci et al 2020 ; Morón-Alfonso et al 2021 ; Peterman et al 2021 ; Peterman and Ritterbush 2022 ).…”

“…3D ) were termed planktic drifters and vertical migrants, respectively. Nektic life habits are supported for oxycones because they generally experience lower hydrodynamic drag (at higher Reynolds numbers) and have superior coasting efficiency ( Jacobs 1992 ; Hebdon et al 2021 ; Hebdon, Ritterbush et al 2022 ; Peterman and Ritterbush 2022 ; Ritterbush and Hebdon 2022 ). However, a growing body of work is demonstrating that serpenticones and sphaerocones did not necessarily experience physical constraints that would have confined them to planktic life habits.…”

Updating studies of past life and ancient ecologies using defossilized organismal proxies

“…PDOP Crofts and Summers, (2014) The determine the buoyancy and mass distributions of organisms submerged in water (Peterman et al, 2019a). Others have performed computational fluid dynamics (CFD) simulations on similar models to determine aero-and hydrodynamic drag, lift, and movement capabilities (Rahman, 2017;Hebdon et al, 2020a;Hebdon et al, 2020b). VDOPs have also been used to study structural resistance to mechanical stress (Lemanis et al, 2016;Lemanis and Zlotnikov, 2018;Lemanis, 2020), bite force (Rayfield, 2007;Walmsley et al, 2013;Cox et al, 2015), and other properties with various finite element analysis (FEA) utilities (Bright, 2014).…”