Piecing together the puzzle of the Ediacara Biota: Excavation and reconstruction at the Ediacara National Heritage site Nilpena (South Australia)

Slime travelers: Early evidence of animal mobility and feeding in an organic mat world

“…If footprints formed via passive transport, they should exhibit predominantly linear arrangements (Sperling & Vinther, ). When preserved on the same bedding plane, they are also expected to be aligned with respect to paleocurrent directionality, as has been observed for other current derived Ediacaran features (Droser et al, ; Evans et al, ; Paterson, Gehling, Droser, & Bicknell, ; Tarhan, Droser, & Gehling, ). This is distinct from the preferred orientation predicted in the active mobility hypothesis: Mobile organisms move in a preferred direction (i.e., forward) but they do not necessarily move in the same direction as their neighbors or paleocurrent.…”

“…Ediacara fossils have been recovered from outcrops of the Ediacara Member in the Flinders Ranges and surrounding regions, with extensive collections housed in the South Australia Museum in Adelaide. Importantly, at the National Heritage Nilpena Ediacara fossil site, located west of the Flinders Ranges, thousands of in situ Ediacaran fossils have been recovered (Droser & Gehling, ; Droser et al, ). Because fossils are best preserved on the base of Ediacara Member beds, systematic excavation and reassembly of bedding plane surfaces are necessary and haves resulted in the reconstruction of more than 300 m 2 of in situ Ediacaran paleocommunities from the ORS and FLLRS Facies (see Droser et al, for a detailed discussion).…”

“…Textured organic surfaces can be preserved as discrete, iterated structures such as the classic “old elephant skin” (Figure a), analogous to micro‐topography found in modern eutrophic ponds, or as dense accumulations of microscopic and macroscopic organisms (Figure b; Gehling & Droser, ). Such aggregations cover meter to decimeter scale bedding planes without definitive outlines or margins (Droser et al, ; Gehling & Droser, ; Tarhan, Droser, Gehling, & Dzaugis, ). Examination of TOS from the Ediacara Member indicates that mat surfaces were remarkably diverse, ubiquitous, and heterogeneously distributed across the Ediacaran seafloor (Droser, Gehling, & Jensen, ; Droser et al, ; Gehling & Droser, ; Tarhan et al, ).…”

“…Lifted, transported, and ripped specimens indicate that Dickinsonia was composed of a relatively resilient outer membrane for a soft‐bodied organism (Evans, Droser, & Gehling, ; Gehling et al, ; Seilacher, ). Size frequency distributions from multiple, distinct excavated bedding planes demonstrate that body fossils of Dickinsonia are not clustered into similarly sized cohorts, interpreted as evidence for continuous reproduction (Darroch, Laflamme, & Clapham, ; Evans, ; Droser et al, ; Reid, García‐Bellido, Payne, Runnegar, & Gehling, ; although see Zakrevskaya, ). Interpretations of the phylogenetic placement of Dickinsonia have varied (Dzik, ; Glaessner & Wade, ; Retallack, ; Seilacher, Grazhdankin, & Legouta, ; Sperling & Vinther, ; Sprigg, ).…”

“…Biogenic sedimentary structures referred to as mop were left when holdfasts of frond‐like organism, such as Arborea or Charniodiscus , were dragged through and occasionally pulled out of the organic mat substrate, leaving strongly aligned features on the Ediacaran seafloor (Tarhan et al, ). Aligned body fossils of frondose taxa are also found on bedding planes where relatively high energy events have toppled them in an orientation consistent with current flow (Droser et al, ). Incomplete specimens of Dickinsonia reflect the insertion of sand below flat‐lying taxa and are oriented based on paleocurrent directionality (Evans et al, ; Paterson et al, ).…”