Evaluation of hypotheses that relate environmental to evolutionary change across the Ediacaran-Cambrian transition has been hampered by a dearth of sections that preserve both the last appearance of Ediacaran body fossils and the first appearance of Treptichnus pedum within carbonate-rich strata suitable for chemostratigraphic studies. Here, we report two new exceptionally preserved latest Ediacaran fossil assemblages from the Deep Spring Formation at Mount Dunfee, Nevada (USA). Further, we report these occurrences in a high-resolution carbon isotope chemostratigraphic framework, permitting correlation on a regional and global scale. The lower of the two horizons, at the base of the Deep Spring Formation, hosts a body fossil assemblage that includes Gaojiashania, other vermiform body fossils, and possible Wutubus annularis interbedded with Cloudina shell beds. The upper of the two fossil horizons, in the Esmeralda Member of the Deep Spring Formation, contains Conotubus and occurs within the basal Cambrian negative carbon isotope excursion, establishing it as the youngest Ediacaran fossil assemblage discovered to date. This is the first report of Gaojiashania, Conotubus, and Wutubus in Laurentia, extending the known stratigraphic ranges and biogeographic distributions of these taxa to a global scale. These data refine the relative ages of defining characteristics of the Ediacaran-Cambrian boundary and confirm that a large perturbation to the carbon cycle and surface ocean conditions coincided with the extinction of Ediacaran organisms.

Owing to the lack of temporally well-constrained Ediacaran fossil localities containing overlapping biotic assemblages, it has remained uncertain if the latest Ediacaran ( 550-541 Ma) assemblages reflect systematic biological turnover or environmental, taphonomic or biogeographic biases. Here, we report new latest Ediacaran fossil discoveries from the lower member of the Wood Canyon Formation in Nye County, Nevada, including the first figured reports of erniettomorphs, , and other problematic fossils. The fossils are spectacularly preserved in three taphonomic windows and occur in greater than 11 stratigraphic horizons, all of which are below the first appearance of and the nadir of a large negative δC excursion that is a chemostratigraphic marker of the Ediacaran-Cambrian boundary. The co-occurrence of morphologically diverse tubular fossils and erniettomorphs in Nevada provides a biostratigraphic link among latest Ediacaran fossil localities globally. Integrated with a new report of from Namibia, previous fossil reports and existing age constraints, these finds demonstrate a distinctive late Ediacaran fossil assemblage comprising at least two groups of macroscopic organisms with dissimilar body plans that ecologically and temporally overlapped for at least 6 Myr at the close of the Ediacaran Period. This cosmopolitan biotic assemblage disappeared from the fossil record at the end of the Ediacaran Period, prior to the Cambrian radiation.