Water flow simulations using 3D fossil models give new clues to evolution of tiny, ancient marine animals

About 536 million years ago, in 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 about ancient ocean conditions and animal evolution.

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

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

The researchers used micro-computed tomography data of the fossils to create virtual 3D models of each species, then applied computational fluid dynamics to simulate how the flow of seawater would drag and deform the organisms when they were alive.

The simulation results indicate that the two species—and most other sessile millimeter-scale jellyfish at the same time—likely lived in the viscous flow layer, a less turbulent layer of seawater just above the sea floor. In addition, the interradial shape of Hexaconularia was shown to be more structurally stable in the simulations than the tetraradial Tetrapyrgites, suggesting that Hexaconularia may have been better adapted to survive the strongly flowing conditions of the ancient marine shelf.

Posted on Journal of Geophysical Research: Biogeosciencesthe findings are consistent with the fossil record suggesting that tetraradial sessile medusozoans, as well as those with tri-, penta-, or hexaradial symmetry, went extinct about 529 million years ago, but that Hexaconularia and other biradial medusozoans 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 details into such simulations, such as seafloor roughness and the presence of neighboring organisms, to further explore this ancient Medozoic community.

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