A cosmopolitan late Ediacaran biotic assemblage: new fossils from Nevada and Namibia support a global biostratigraphic link

Abstract

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.

Discovery of bilaterian-type through-guts in cloudinomorphs from the terminal Ediacaran Period

“…2). These fossils, as well as others from nearby units, have been taxonomically compared 30 with the well-studied tubular fauna of the Gaojiashan Lagerstätte, South China 26 and, more recently, to lesser-known cloudinomorphs from the East European Platform 6,27 . Systematic investigation of the Wood Canyon cloudinomorph fossils has thus far formally described two new species, Saarina hagadorni and Costatubus bibendi, as the most abundant in this locality 6 .…”

“…The fossils reported here were collected as part of broader studies on the taxonomy 6 and biostratigraphic utility of the tubular fossil assemblages from south-central Nevada 30 . In the Montgomery Mountains, the informal lower member of the Wood Canyon Formation is predominantly interbedded siltstone and sandstone, interpreted to have been deposited in a shallow marine paleoenvironment 30 . Three shallowing-upward parasequences in the lower member, each capped by dolostone marker beds, provide a regionally consistent stratigraphic framework (Fig.…”

New high‐resolution age data from the Ediacaran–Cambrian boundary indicate rapid, ecologically driven onset of the Cambrian explosion

“…A recent study also emphasizes the presence of trace fossils produced by sediment bulldozers in this part of the section, which “may in fact be regarded as a representative of Cambrian‐style bioturbation” (Buatois et al., , p. 3). Simple, Ediacaran‐type traces are represented by Helminthopsis , which are also known from older strata of the Huns Member and the Nudaus Formation, as are the non‐ or poorly mineralized body fossils Gaojiashania and Shaanxilithes (Darroch et al., ; Smith, Nelson, Tweedt, Zeng, & Workman, ). These fossil assemblages indicate a progressive rise of more complex organisms, peaked by the advent of complex and burrowing metazoans responsible for the successive reduction in the extent of microbial mats above a 547.36 ± 0.23 Ma old ash (Bowring et al., ).…”

Subsidence history of the Ediacaran Johnnie Formation and related strata of southwest Laurentia: Implications for the age and duration of the Shuram isotopic excursion and animal evolution

“…), and they have generally not been accepted in subsequent stratigraphic studies of the region (e.g., Loyd et al, 2012Loyd et al, , 2015. Latest Ediacaran fossils have been recovered from the uppermost Stirling Formation and the Lower Member of the Wood Canyon Formation in the Spring Mountains and neighboring Montgomery Mountains to the south (e.g., Cloudina and Swartpuntia; Hagadorn and Waggoner, 2000;Smith et al, 2017), from sections in stratigraphic continuity with the type Johnnie Formation. These are succeeded immediately upward by Lower Cambrian trace fossils (Treptichnus pedum), which places the Ediacaran-Cambrian boundary in the Lower Member of the Wood Canyon Formation ( Fig.…”

“…We used thicknesses from this study combined with thicknesses for overlying formations principally based on Stewart (1970) and Burchfiel et al (1974). Our analysis encompasses known time points ranging from the Ediacaran-Cambrian boundary in the Lower Member of the Wood Canyon Formation (Corsetti and Hagadorn, 2000;Hagadorn and Waggoner, 2000;Smith et al, 2016Smith et al, , 2017 at 541 Ma, up through the Devonian-Mississippian boundary at the top of the Devils Gate Formation (Burchfiel et al, 1974) at 359 Ma (Ogg et al, 2016). The only previous attempt at a geohistory analysis of the Spring Mountains (Levy and Christie-Blick, 1991) was temporally constrained mainly by the Lower-Middle and Middle-Upper Cambrian boundaries, which were then deemed to be ~30 m.y.…”