PUTTING THE FUN IN TAPHONOMY: THE MULTIFACETED ROLE OF FUNISIA DOROTHEA IN THE PRESERVATION OF EDIACARA ECOSYSTEMS

Textured organic surfaces (TOS) are common on bedding planes of the Ediacara Member (Rawnsley Quartzite) cropping out in the Flinders area of South Australia. A high diversity of TOS are found on the 33 excavated beds at the Nilpena National Heritage Ediacara Fossil Site. Of particular abundance are the distinct TOS created by the tube-like organism, Funisia dorothea. Funisia is the most abundant fossil found at Nilpena and commonly occurs as a dense TOS, covering entire bedding planes in the Oscillation Rippled Sandstone (ORS) and Planar-Laminated and Rip-Up Sandstone (PLRUS) facies.

When alive, Funisia formed dense stands of tubes extending up into the water column. Upon death, the collapsed tubes created thick TOS on the ocean floor. This dichotomy of seafloor occupation likely led Funisia to be a primary ecologic and taphonomic control. To assess the nature of Funisia’s impact, we studied nine Funisia-dominated beds at Nilpena from ORS and PLRUS facies. Funisia fabrics were characterized with an emphasis on taphonomy, dimensions of well-preserved tubes, and preservation of associated taxa. In both the ORS and PLRUS facies, beds were found to be dominated by specific Funisia taphomorphs that were diagnosed by the integrity of tube structures. This allowed us to place each bed on a spectrum of preservation based on the bed’s dominant taphomorph.

End members of the preservational spectrum correspond to the timing of death and burial of Funisia. At one end of the spectrum, beds are dominated by well-preserved Funisia taphomorphs, in which the time of death was the same as the time of burial (TD=TB). When TD=TB, Aspidella is the only organism shown to live alongside Funisia; benthic organisms are not present because their colonization was prevented by dense stands of Funisia and frondose organisms. At the other end of the spectrum, beds are dominated by “ghost” Funisia taphomorphs, in which Funisia are very poorly preserved. Here, a maximum amount of time elapsed after Funisia death (TD≠TB). When TD≠TB, beds exhibit the highest diversity of additional benthic organisms because taxa such as Dickinsonia, Spriggina, and Tribrichidium had time to move in on top of the TOS, resulting in a time-averaged assemblage.