FUNCTIONAL MORPHOLOGY OF THE EDIACARAN ORGANISM TRIBRACHIDIUM HERALDICUM REVEALED BY COMPUTATIONAL FLUID DYNAMICS

The latest Ediacaran (~575–539 Ma) directly precedes the Cambrian and has long been thought to consist of simple ecosystems dominated by organisms that fed by osmotrophy (i.e., direct absorption of dissolved organic compounds) (Laflamme et al., 2014). However, recent studies have consistently demonstrated higher ecosystem complexity and a broader range of feeding modes than previously appreciated (Darroch et al., 2017). Among the most bizarre and historically confounding Ediacaran species is Tribrachidium heraldicum—an approximately hemispherical organism exhibiting tri-radial symmetry with three arms that spiral counter-clockwise from its center (Hall et al., 2015). Rahman et al. (2015) used a 3D Tribrachidium model generated from CT scanning to simulate water flow around the organism, finding flow patterns suggestive of suspension feeding rather than osmotrophy. However, this model was relatively crude, lacking key anatomical features present in well-preserved fossils. We expand on this research using 3D models constructed with CAD software which include important morphological characters missing from earlier models. In addition, we investigate the effects of specific anatomical features as possible controls on fluid flow patterns using a range of null models. Lastly, the results are compared to potential modern analogues thought to feed in a similar fashion. By applying highly-fidelity CFD methods on this expanded set of more accurate models, we gain further insight into the paleobiology and functional morphology of an iconic Ediacaran organism and the potential role played by suspension feeding in structuring late Ediacaran benthic communities.