A biomechanical approach to Ediacaran hypotheses: how to weed the Garden of Ediacara

Flume experiments and analytical approaches are undertaken to determine the stability of flat-lying Ediacaran organisms in fluid flow. Organisms such as Dickinsonia would not have been viable if reconstructed as free-living worms or syncytia. Models of flat-lying Ediacarans occupying a range of densities well beyond those of suggested modern analogs were dislodged by fluid flow taken as typical of Ediacaran paleoenvironments. Analytical tests suggest that parameters such as thickness of the organism and its coefficient of friction have little effect over the range of flows being considered here. These results lead to four non-exclusive interpretations of fossils of flat-lying Ediacarans: (1) The organisms have been transported from a quieter environment (in which case their pristine preservation is similarly puzzling); (2) they had a density approaching that of a flatfish; (3) they were secured to the substrate in some manner; (4) they lived partially or wholly beneath the substrate surface.