Water flow simulations using 3D fossil models provide new clues about the evolution of tiny ancient marine animals

About 536 million years ago, during the early Cambrian Period, an abundance of different species of millimeter-scale marine organisms thrived in continental shelf habitats around the world. Today, their fossils provide clues to ancient ocean conditions and animal evolution.

Many of these tiny fossils are sedentary jellyfish, a subgroup of the phylum Cnidaria that now includes free-swimming jellyfish. New research by Ping Liu and his colleagues reveals for the first time how the exoskeletal forms of ancient, tiny jellyfish may have interacted with flowing water in their marine shelf environment.

The researchers collected fossils of two species, Hexaconularia sichuanensis and Quadrapyrgites quadratacris, from the 535-million-year-old Kuanchuanpu Formation in southern China’s Shaanxi province. The fan shape of Hexaconularia exhibits biradial symmetry, while Quadrapyrgites is tetraradial.

The researchers used microcomputer tomography data from the fossils to create virtual 3D models of each species, then applied computational fluid dynamics to simulate how the flow of seawater would have dragged and deformed the organisms as they were alive.

The simulation results suggest that both species—and most other sedentary millimeter-scale medusozoans from the same era—probably lived in the Viscous Flow Layer, a layer of less turbulent seawater just above above the seabed. Additionally, the biradial form of Hexaconularia was found to be more structurally stable in the simulations than the tetraradial Quadrapyrgites, suggesting that Hexaconularia might have been better adapted to survive the high flow conditions of the ancient sea shelf. .

Posted in the Journal of Geophysical Research: Biogeosciencesthe findings are consistent with the fossil record suggesting that sedentary tetraradial jellyfish, as well as those with tri-, penta-, or hexaradial symmetry, became extinct around 529 million years ago, but that Hexaconularia and other biradial jellyfish have survived.

This study marks the first application of computational fluid dynamics to Early Cambrian microfossils living in the viscous flow layer. The authors suggest that future research could introduce more detail into such simulations, such as seafloor roughness and the presence of nearby organisms, to further explore this ancient jellyfish community.

This story is republished courtesy of Eos, hosted by the American Geophysical Union. Read the original story here.