TAXONOMIC EVALUATION OF A TUBULAR ASSEMBLAGE FROM THE TERMINAL EDIACARAN OF NEVADA

The terminal Ediacaran Period (~551–541 Ma) is home to a unique tubular fauna, distinct from both the earlier communities of macroscopic Ediacara biota and the later complex ecosystems of the Cambrian Period. Tubular forms, including cloudinids (i.e., Cloudina, Conotubus, and Sinotubulites), are well-described from such localities as the Gaojiashan lagerstätte, South China. While Cloudina may have been the most widely distributed paleogeographically, new discussions of broader cloudinids from Nye and Esmeralda counties (Wood Canyon and Deep Spring formations, respectively), Nevada, USA (Smith et al., 2016, 2017), are reinvigorating the discussion of shelly tubes in the terminal Ediacaran. With initial reports of several tubular taxa from these Nevada localities, the onus now shifts towards providing a thorough taxonomic assessment of these fossils to better frame their presumed equivalence to other Ediacaran localities globally. Here, we provide detailed characterization, using a combination of optical microscopy, scanning electron microscopy, and x-ray microscopy, of two tubular, pyritized cloudinids from both Nevada localities. We describe a new species of the genus Conotubus, with its nested funnel-in-funnel tubular construction and a presumed lightly to nonbiomineralized tube. Apart from well-characterized species of Conotubus in China, however, the Nevada examples are significantly smaller in funnel diameter and show less detail on the funnels themselves, warranting the establishment of a new species. The second newly erected taxon also shows a nested tubular construction, and may be easily confused as a taphomorph of Conotubus. This new taxon, here named Costatubus gen. nov., is comprised of nested, repeating barrel-shaped units, and shows evidence of original biomineralization in the form of brittle fracture during compression. The broader Nevada tubular community may show comparable taxonomic diversity to that of the Gaojiashan biota, and may thus comprise important localities for understanding the global ecology of the tubular fauna in the terminal Ediacaran Period.