Dickinsonia liftoff: Evidence of current derived morphologies.

Dickinsonia , an iconic member of the Ediacara biota, is abundant in the Ediacaran deposits found at the Nilpena field site, South Australia. Despite exquisite fossil preservation at this site, many specimens of Dickinsonia appear to be incomplete, with an apparently “missing piece” on the periphery. Orientation measurements from specimens on three fossil beds suggest that these so-called “missing pieces” are aligned irrespective of the axial orientation of Dickinsonia . The nonrandom orientation of incomplete specimens matches that of other aligned structures found on two of these beds. The preferred directionality of this feature suggests the molding of incomplete specimens under the influence of current activity prior to or during burial. We propose that this feature originates where part of a Dickinsonia was lifted off of the substrate during a storm event and that sand was deposited beneath this lifted portion. This model suggests that Dickinsonia was easily separated from the sea floor and was not attached to the substrate on which it lived. This is consistent with the data from Dickinsonia footprints suggesting that Dickinsonia was mobile. [ABSTRACT FROM AUTHOR]