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The Nama Group of Namibia and South Africa preserves an extraordinary record of marine ecosystems existing in the lastc. 15 myr of the Ediacaran, comprising enigmatic and soft-bodied fossils that are part of the first major radiation of macroscopic life. Since their description at the beginning of the 20th century these fossils have played an important role in debates surrounding the affinities of iconic Ediacaran fossil groups, and ash beds preserved throughout the succession have been crucial to understanding rates and patterns of early animal evolution. Fossils preserved in varying contexts have allowed for detailed reconstructions of Ediacaran palaeobiology, and geochemical analyses provide a window into understanding the controls on Ediacaran taphonomic pathways, including crucial, and potentially widespread, roles played by clay minerals in exceptional fossil preservation. 

Abstract Tribrachidium heraldicumis an Ediacaran body fossil characterized by triradial symmetry. Previous work has suggested that the anatomy ofTribrachidiumwas conducive to passive suspension feeding; however, these analyses used an inaccurate model and a relatively simple set of simulations. Using computational fluid dynamics, we explore the functional morphology ofTribrachidiumin unprecedented detail by gauging how the presence or absence of distinctive anatomical features (e.g., apical pits and arms) affects flow patterns. Additionally, we map particle pathways, quantify deposition rates at proposed feeding sites, and assess gregarious feeding habits to more fully reconstruct the lifestyle of this enigmatic taxon. Our results provide strong support for interpretingTribrachidiumas a macroscopic suspension feeder, with the apical pits representing loci of particle collection (and possibly ingestion) and the triradial arms representing morphological adaptations for interrupting flow and inducing settling. More speculatively, we suggest that the radial grooves may represent ciliated pathways through which food particles accumulating in the wake of the organism were transported toward the apical pits. Finally, our results allow us to generate new functional hypotheses for other Ediacaran taxa with a triradial body plan. This work refines our understanding of the appearance of suspension feeding in shallow-water paleoenvironments, with implications for the radiation of Metazoa across the Ediacaran/Cambrian boundary.