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

Abstract

Externally shelled cephalopods with coiled, planispiral conchs were ecologically successful for hundreds of millions of years. These animals displayed remarkable morphological disparity, reflecting comparable differences in physical properties that would have constrained their life habits and ecological roles. To investigate these constraints, self-propelling, neutrally buoyant, biomimetic robots were 3D-printed for four disparate morphologies. These robots were engineered to assume orientations computed from virtual hydrostatic simulations while producing Nautilus-like thrusts. Compressed morphotypes had improved hydrodynamic stability (coasting efficiency) and experienced lower drag while jetting backwards. However, inflated morphotypes had improved maneuverability while rotating about the vertical axis. These differences highlight an inescapable physical tradeoff between hydrodynamic stability and yaw maneuverability, illuminating different functional advantages and life-habit constraints across the cephalopod morphospace. This tradeoff reveals there is no single optimum conch morphology, and elucidates the success and iterative evolution of disparate morphologies through deep time, including non-streamlined forms.

Stability–Maneuverability Tradeoffs Provided Diverse Functional Opportunities to Shelled Cephalopods

“…; 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 ). Nautilids—the only living cephalopods with chambered, external conchs—are frequently used as models for the swimming capabilities and function of extinct taxa.…”

“…The living animals are more hydrostatically stable when these two centers are farther separated. Generally, planispiral conchs with larger body chamber proportions have lower hydrostatic stability ( Raup 1967 ; Saunders and Shapiro 1986 ; Hoffmann et al 2015 ; Lemanis et al 2015 ; Peterman and Ritterbush 2022 ). Extant nautilids have short body chambers and are regarded as hydrostatically stable objects.…”

“…A Reconstruction of a serpenticone cephalopod (resembling the ammonoid, Dactylioceras commune with no ornament). B Virtual hydrostatic model of a serpenticone ammonoid, modified from Peterman and Ritterbush 2022 ). C Fully assembled, 3D-printed model with tracking points placed along the vertical axis passing through the hydrostatic centers (see Fig.…”

A Plea for a New Synthesis: From Twentieth-Century Paleobiology to Twenty-First-Century Paleontology and Back Again

“…Scientists are working together with engineers to model and construct bio-inspired robots to understand evolution. One example above all (for another example published recently, see [ 55 ]) is given by research on the morphology of Orobates pabsti . This is a four-legged vertebrate organism that went extinct about 300 million years ago.…”

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

“…Experiments using DOPs are frequently interdisciplinary, generating results that investigators can apply across ecology, evolution, engineering, paleontology, and other fields in several ways: 1) Collecting empirical data allows investigators to assess the potential function of morphology and hypothesize about its adaptive value, if any, exists. For example, DOPs can be used to evaluate morphological tradeoffs between different roles, like defense and locomotion (Johnson, 2020) or stability and maneuverability (Peterman and Ritterbush, 2022). Functional experimental studies are also valuable to modern animal behaviorists interested in evolutionary processes governing behaviors (Hsieh and Plotnick, 2020).…”