Ancient life and moving fluids

Abstract

Over 3.7 billion years of Earth history, life has evolved complex adaptations to help navigate and interact with the fluid environment. Consequently, fluid dynamics has become a powerful tool for studying ancient fossils, providing insights into the palaeobiology and palaeoecology of extinct organisms from across the tree of life. In recent years, this approach has been extended to the Ediacara biota, an enigmatic assemblage of Neoproterozoic soft‐bodied organisms that represent the first major radiation of macroscopic eukaryotes. Reconstructing the ways in which Ediacaran organisms interacted with the fluids provides new insights into how these organisms fed, moved, and interacted within communities. Here, we provide an in‐depth review of fluid physics aimed at palaeobiologists, in which we dispel misconceptions related to the Reynolds number and associated flow conditions, and specify the governing equations of fluid dynamics. We then review recent advances in Ediacaran palaeobiology resulting from the application of computational fluid dynamics (CFD). We provide a worked example and account of best practice in CFD analyses of fossils, including the first large eddy simulation (LES) experiment performed on extinct organisms. Lastly, we identify key questions, barriers, and emerging techniques in fluid dynamics, which will not only allow us to understand the earliest animal ecosystems better, but will also help to develop new palaeobiological tools for studying ancient life.

The Importance of Size and Location Within Gregarious Populations of Ernietta plateauensis

“…Because LES is more accurate and time-dependent, it allowed for more precisely resolved fluid flow patterns in the more complex population setup; however, the time required to solve LES simulations limited its use in idealized populations. For a more in-depth discussion the benefits of LES over RANS, see Gibson et al (2021). For a more in-depth discussion of turbulence models in general, see Blazek (2001).…”

“…Following previous setups (e.g., Rahman, 2017), our seafloor and Ernietta individuals were assigned no-slip conditions (e.g., fixing the velocity at 0 m/s), the upper face and flow-parallel faces were assigned slip conditions, and the inlet and outlet conditions were assigned on the upstream and downstream faces, respectively. For the inlet boundary condition, a fully-developed, depth-averaged velocity was prescribed (Gibson et al, 2021), and a zero-pressure condition was assigned to the outlet. We chose U 0.1, 0.2, 0.5 m/s following previous Ernietta CFD analyses (Gibson et al, 2019).…”

Adaptation to a Viscous Snowball Earth Ocean as a Path to Complex Multicellularity

“…The Ediacaran fauna lived in a complex fluid environment (Darroch et al 2018;Ghisalberti et al 2014;Rahman et al 2015;Gibson et al 2021). Filter feeding sponges are likely to have made their first appearance in the interlude between the Sturtian and Marinoan glaciations (Gold et al…”

Functional assessment of morphological homoplasy in stem-gnathostomes

“…The shear stress transport (SST) turbulence model and a segregated solver algorithm were used to solve the Reynolds averaged Navier-Stokes (RANS) equations. The choice of the RANS SST model is based on its reduced computational requirements and potential for capturing the same general flow patterns than other more refined models (e.g., large eddy simulation) [40]. Segregated iterations terminated when the relative error was lower than the relative tolerance (0.001).…”

“…The choice of the RANS SST model is based on its reduced computational requirements and potential for capturing the same general flow patterns than other more refined models (e.g. large eddy simulation) [41]. Segregated iterations terminated when the relative error was lower than the relative tolerance (0.001).…”