Resolving taphonomic biases in lower Cambrian shelly fossil assemblages of the Mernmerna Formation, South Australia
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[EMBARGOED UNTIL 12/01/2026] During the earliest Cambrian, a diverse group of small shelly faunas (SSFs) emerged, whose remains have been used to infer animal phylogenetic affinities, paleoecology, as well as to serve as valuable biostratigraphic markers. This record owes its high resolution to the pervasive phosphatization of several SSFs, yielding exceptional morphological detail, though also exhibiting selective taphonomic biases. In the MMF TAPH section of the Mernmerna Formation (Cambrian Series 2, Stage 3) in the Bunkers Range of South Australia, we quantify sources of introduced bias and assess their implications for interpreting the paleoecology and paleobiology of SSF assemblages. The study of SSF typically relies on destructive acid maceration to extract microfossils from host limestone. As effective as this process is for isolating fossils with insoluble elements (particularly phosphate), it preferentially dissolves calcareous material that may be present. In the first of two case studies, paired destructive and non-destructive methodologies reveal that this dissolution introduces taxonomic and mineralogical biases into the fossil assemblages obtained. The second case study focuses on a specific enigmatic microfossil, Stoibostrombus crenulatus, whose organismal affinity has eluded confident taxonomic placement. Using comparative anatomy in tandem with various microimaging techniques, we conducted a detailed examination of S. crenulatus, fossil priapulids, and the modern Priapulus caudatus, which supports a potential affinity between the fossil sclerites and the scalids of priapulid worms.
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M.S.