Biostratinomy of the enigmatic tubular organism Aulozoon soliorum, the Rawnsley Quartzite, South Australia

Abstract

The Ediacaran fauna (574–539 Ma) are the first macroscopic community forming organisms on Earth, thus providing unique insight into the origins and evolution of complex life. However, the assignment of most Ediacaran organisms to specific phyla and kingdoms remains difficult due to their commonly non-analogous body plans and soft-bodied nature, which often results in the loss of diagnostic features through the processes of death and fossilization. Notably, this taphonomic overprint is not imparted equally to all Ediacaran organisms and is particularly exaggerated for the morphotypic grouping of tubular organisms. This morphogroup is comprised of macroscopic organisms with elongate, hollow, and simple body plans and is the most abundant Ediacaran morphogroup. However, the simple and hollow morphology of tubular organisms results in a broadly low preservation potential. In turn, this commonly limits the reconstruction of in vivo morphology, muddles taxonomic assignment, obfuscates phylogenetic affinities, and inhibits understanding of their broader significance. Fortunately, previous studies of abundant tubular taxa have demonstrated that taxon-level biostratinomic investigations can, in part, account for this low preservation potential. Such studies inform a more complete understanding of the morphogroup, providing novel insight into the paleobiology, paleoecology, and biomaterials of tubular taxa. To contribute to this biostratinomically-geared assessment of Ediacaran tubular organisms, this study analyzes the preservation of Aulozoon soliorum, an abundant tubular organism from the Rawnsley Quartzite of South Australia. This investigation demonstrates that Aulozoon is preserved via five preservational modes, which inform a novel in vivo reconstruction of Aulozoon as a sessile, fluid-filled, cylindrical organism with a holdfast and a thin, organic, and featureless body wall. The preservational modes identified here additionally inform a taphonomic framework under which Aulozoon fossils can be interpreted, thus furthering holistic understanding of the morphogroup-specific preservational variability of Ediacaran tubular organisms.