NEW DATA ON CLOUDINIDS FROM THE TERMINAL EDIACARAN OF NEVADA: POSSIBLE SOFT-TISSUE PRESERVATION MAY PROVIDE CLUES ONTO PHYLOGENETIC POSITION (Invited Presentation)

The terminal interval of the Ediacaran Period (~551–541 Ma) represents a turning point in the evolution of complex multicellular eukaryotes. Uniquely positioned between the peak diversity of classic Ediacarans and the subsequent rise of true metazoans during the Cambrian explosion, the fossil record of the terminal Ediacaran exhibits communities comprised of multiple taxa with broadly tubular morphologies, including the well-known index fossil Cloudina. These generally small, tubular organisms may not look as remarkable as those temporally on either side of their prevalence, but they bore witness to several significant ecological and environmental events, including the origins of macro-scale biomineralization and predation. Given their pivotal role in the advent of biomineralization, these tubes, although phylogenetically uncertain at present, may serve as an evolutionary bridge across the Ediacaran–Cambrian transition. Here, we investigate terminal Ediacaran tubular taxa from the Deep Spring and Wood Canyon formations, Esmeralda and Nye counties (respectively), Nevada, USA. From our analyses, we have characterized these tubular fossils both taxonomically (see Selly et al., 2018 GSA Abstracts and Programs) and taphonomically. Using a combination of optical microscopy, scanning electron microscopy, energy dispersive x-ray spectrometry, and x-ray microscopy, we confirm preservation through pyritization—comparable to similar tubular taxa of the Gaojiashan lagerstätte, South China—and report the presence of potential soft tissues within their outer tube walls. The soft tissues reported manifest as internal tubular structures, mm-scale in diameter and hollow-to-pyrite-infilled, that extend through the majority of the outer structural tube. Compared to modern tube-dwelling polychaetes (Family Sabellidae), these preserved features are too small to represent the full body of the Ediacaran tube-dwellers, but instead are comparable in body-size proportion and central position to a digestive system. While not a smoking gun, these organisms may show the oldest gut in the fossil record, which would better phylogenetically place the cloudinids with true coelomates as opposed to alternative interpretations as acoelomate cnidarians with simple digestive cavities or algae.