Hydrodynamic Simulations of Millimeter‐Scale Cambrian Sedentary Medusozoans

• Published in: Journal of geophysical research. Biogeosciences Vol. 127; no. 10
• Main Authors: Liu, Ping, Zhang, Yiheng, Yang, Xiaoguang, Wang, Bin, Zhang, Tao, Sun, Jie, Tang, Qingqin, He, Kaiyue, Hao, Wenjing, Yue, Ning, He, Xiaowei, Han, Jian
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-10-2022
• Subjects: 3D mesh model; Benthos; Cambrian; Computational fluid dynamics; Computer applications; Dynamic structural analysis; early Cambrian; Exoskeleton; Exoskeletons; Finite element method; Fluid dynamics; Fluid-structure interaction; Food chains; Food webs; Fossils; Functional morphology; hydrodynamic simulations; Hydrodynamics; kuanchuanpu formation; Marine organisms; Mathematical models; medusozoan; Microorganisms; Morphology; Natural selection; Physical characteristics; sedentary life; Shelving; Simulation; Swimming; Symmetry; Three dimensional models; Tidal currents; Tidal flow; Viscous sublayers; Water flow
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2022JG006854

Modern medusae are primarily macroscopic, free‐swimming marine organisms with a tetraradial symmetry. But the early Cambrian medusozoans, such as biradial Hexaconularia sichuanensis and tetraradial Quadrapyrgites quadratacris from the basal Cambrian Kuanchuanpu Formation in South China, were millimeter‐scale and sedentary forms. Although well‐documented as common components in a shelf environment, little is known about their in situ life conditions since they are easily transported by tidal flow before burial. Specifically, the interactions between their exoskeleton shapes and the hydrodynamic conditions are poorly known. Here we use fluid–structure interaction computational fluid dynamics to analyze the functional performance of the two taxa using 3D mesh models constructed from scanned fossils. The simulation experiments reveal that: (a) due to their millimeter‐scale size, most sedentary small shelly fossils (SSFs), including those of medusozoans lived within the viscous sublayer range of tidal flow; (b) the biradial symmetry of Hexaconularia was more structurally stable than the tetraradial symmetry of Quadrapyrgites; (c) different orientations of Hexaconularia, relative to the water flow, resulted in different force distributions on the surface. This research provides quantitative data of the hydrodynamic conditions of SSFs in shelf environments and critical insights into the biotic replacement of the early Cambrian benthic medusozoan community.
Plain Language Summary
Computational fluid dynamics (CFD) method in recent 5 years has been proved to be an effective tool to address functional morphology of macrofossils. However, it has never been applied to microfossils, particularly those from the early Cambrian, which have played increasingly important roles in understanding the origin of animal phyla and stepwise establish of complex food web during the Ediacaran‐ Cambrian transitional period. In this study we examined the fluid dynamics of millimeter‐scale sedentary medusozoan fossils (Quadrapyrgites quadratacris and Hexaconularia sichuanensis) from the Cambrian Kuanchuanpu Formation in South Chian using 3D mesh models and computational fluid dynamics. The results reveal that even microscopic morphological characteristics (shapes, symmetry patterns and orientations) can lead to significant differences in hydrodynamic effects, which may exert further influence on their lifestyles and evolution. This research first introduces CFD to the field of early Cambrian microfossils and paves the way for more sophisticated simulations in the future, leading us to a better understanding of the role hydrodynamics played in the natural selection of early Cambrian sedentary benthos.
Key Points
Hydrodynamics related with the viscous flow layer profoundly affected the Cambrian millimeter‐scale benthic medusozoans
The biradial symmetry is more adaptable to shelf environments than the tetraradial form
This could help to explain the biotic replacement of the early Cambrian benthic medusozoan community