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Abstract We describe > 200 ribbon-like macroscopic fossils from terminal Ediacaran strata at Mount Dunfee, Nevada, USA ∼ 115 m below the local placement of the Ediacaran–Cambrian boundary. They are preserved as casts and molds, composed of Fe-oxides and Fe-rich aluminosilicates in an aluminosilicate clay matrix. Measurements of 50 of the specimens provide a fossil size range of 0.22–0.74 mm-wide and 0.1–75.0 mm-long. Some specimens evidence original flexibility and appear to be fragmented, consistent with soft body preservation. They are therefore interpreted as body fossils, rather than trace fossils. Given this interpretation, we suggest that the fossils’ size range and ribbon-like morphologies are consistent with them being members of the problematicum Vendotaenia, which have not been previously reported from Ediacaran strata within the southern Great Basin. The phylogenetic affinity of vendotaenids is unresolved, but they are commonly interpreted as a form of eukaryotic macroalgae. This report firmly establishes vendotaenids in Ediacaran strata on Laurentia, broadening their known paleogeographic range during the end-Ediacaran Period. Additionally, the morphology of the fossils described here supports the notion that, although vendotaenids are reported from many Ediacaran paleocontinents globally, there was low macroalgal diversity at the end of the Ediacaran Period. 

The geologically rapid appearance of fossils of modern animal phyla within Cambrian strata is a defining characteristic of the history of life on Earth. However, temporal calibration of the base of the Cambrian Period remains uncertain within millions of years, which has resulted in mounting challenges to the concept of a discrete Cambrian explosion. We present precise zircon U–Pb dates for the lower Wood Canyon Formation, Nevada. These data demonstrate the base of the Cambrian Period, as defined by both ichnofossil biostratigraphy and carbon isotope chemostratigraphy, was younger than 533 Mya, at least 6 My later than currently recognized. This new geochronology condenses previous age models for the Nemakit–Daldynian (early Cambrian) and, integrated with global records, demonstrates an explosive tempo to the early radiation of modern animal phyla. 

The Ediacaran−Cambrian boundary strata in the Great Basin of the southwestern United States record biological, geochemical, and tectonic change during the transformative interval of Earth history in which metazoans diversified. Here, we integrate new and compiled chemostratigraphic, paleontological, sedimentological, and stratigraphic data sets from the Death Valley region, the White-Inyo Ranges, and Esmeralda County in Nevada and California and evaluate these data within a regional geologic framework. A large negative carbon isotope (δ13C) excursion—also known as the Basal Cambrian Excursion, or BACE—is regionally reproducible, despite lateral changes in sedimentary facies and dolomitization across ∼250 km, consistent with a primary marine origin for this perturbation. Across the southern Great Basin, Ediacaran body fossils are preserved in a variety of taphonomic modes, including cast and mold preservation, two-dimensional compressional preservation, two-dimensional and three-dimensional pyritization, and calcification. The stratigraphic framework of these occurrences is used to consider the relationships among taphonomic modes for fossil preservation and paleoenvironmental settings within this basin. In this region, Ediacaran-type fossils occur below the nadir of the BACE, while Cambrian-type trace fossils occur above. Sedimentological features that include giant ooids, stromatolites, and textured organic surfaces are widespread and abundant within the interval that records biotic turnover and coincide with basaltic volcanism and the BACE. We hypothesize that the prevalence of these sedimentological features, the BACE, and the disappearance of some Ediacaran clades were caused by environmental perturbation at the Ediacaran-Cambrian boundary.