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The origin of motility in bilaterian animals represents an evolutionary innovation that transformed the Earth system. This innovation probably occurred in the late Ediacaran period—as evidenced by an abundance of trace fossils (ichnofossils) dating to this time, which include trails, trackways and burrows 1 – 3 . However, with few exceptions 4 – 8 , the producers of most of the late Ediacaran ichnofossils are unknown, which has resulted in a disconnection between the body- and trace-fossil records. Here we describe the fossil of a bilaterian of the terminal Ediacaran period (dating to 551–539 million years ago), which we name Yilingia spiciformis (gen. et sp. nov). This body fossil is preserved along with the trail that the animal produced during a death march. Yilingia is an elongate and segmented bilaterian with repetitive and trilobate body units, each of which consists of a central lobe and two posteriorly pointing lateral lobes, indicating body and segment polarity. Yilingia is possibly related to panarthropods or annelids, and sheds light on the origin of segmentation in bilaterians. As one of the few Ediacaran animals demonstrated to have produced long and continuous trails, Yilingia provides insights into the identity of the animals that were responsible for Ediacaran trace fossils. Yilingia spiciformis , a bilaterian dating to the Ediacaran period, is described from body fossils associated with trails produced by the animal, shedding light on the origins of segmentation and motility in bilaterian animals.

After nearly a billion years with no evidence for glaciation, ice advanced to equatorial latitudes at least twice between 717 and 635 Mya. Although the initiation mechanism of these Neoproterozoic Snowball Earth events has remained a mystery, the broad synchronicity of rifting of the supercontinent Rodinia, the emplacement of large igneous provinces at low latitude, and the onset of the Sturtian glaciation has suggested a tectonic forcing. We present unique Re-Os geochronology and high-resolution Os and Sr isotope profiles bracketing Sturtian-age glacial deposits of the Rapitan Group in northwest Canada. Coupled with existing U-Pb dates, the postglacial Re-Os date of 662.4 ± 3.9 Mya represents direct geochronological constraints for both the onset and demise of a Cryogenian glaciation from the same continental margin and suggests a 55-My duration of the Sturtian glacial epoch. The Os and Sr isotope data allow us to assess the relative weathering input of old radiogenic crust and more juvenile, mantle-derived substrate. The preglacial isotopic signals are consistent with an enhanced contribution of juvenile material to the oceans and glacial initiation through enhanced global weatherability. In contrast, postglacial strata feature radiogenic Os and Sr isotope compositions indicative of extensive glacial scouring of the continents and intense silicate weathering in a post–Snowball Earth hothouse.

The Neoproterozoic was an era of great environmental and biological change, but a paucity of direct and precise age constraints on strata from this time has prevented the complete integration of these records. We present four high-precision U-Pb ages for Neoproterozoic rocks in northwestern Canada that constrain large perturbations in the carbon cycle, a major diversification and depletion in the microfossil record, and the onset of the Sturtian glaciation. A volcanic tuff interbedded with Sturtian glacial deposits, dated at 716.5 million years ago, is synchronous with the age of the Franklin large igneous province and paleomagnetic poles that pin Laurentia to an equatorial position. Ice was therefore grounded below sea level at very low paleolatitudes, which implies that the Sturtian glaciation was global in extent.

The Silurian-age rise of land plants is hypothesized to have caused a global revolution in the mechanics of rivers. In the absence of vegetation-controlled bank stabilization effects, pre-Silurian rivers are thought to be characterized by shallow, multithreaded flows, and steep river gradients. This hypothesis, however, is at odds with the pancontinental scale of early Neoproterozoic river systems that would have necessitated extraordinarily high mountains if such river gradients were commonplace at continental scale, which is inconsistent with constraints on lithospheric thickness. To reconcile these observations, we generated estimates of paleogradients and morphologies of pre-Silurian rivers using a well-developed quantitative framework based on the formation of river bars and dunes. We combined data from previous work with original field measurements of the scale, texture, and structure of fluvial deposits in Proterozoic-age Torridonian Group, Scotland—a type-example of pancontinental, prevegetation fluvial systems. Results showed that these rivers were low sloping (gradients 10−5 to 10−4), relatively deep (4 to 15 m), and had morphology similar to modern, lowland rivers. Our results provide mechanistic evidence for the abundance of low gradient, single-threaded rivers in the Proterozoic eon, at a time well before the evolution and radiation of land plants—despite the absence of muddy and vegetated floodplains. Single-threaded rivers with stable floodplains appear to have been a persistent feature of our planet despite singular changes in its terrestrial biota.

Fossilized carotenoid hydrocarbons provide a window into the physiology and biochemistry of ancient microbial phototrophic communities for which only a sparse and incomplete fossil record exists. However, accurate interpretation of carotenoid-derived biomarkers requires detailed knowledge of the carotenoid inventories of contemporary phototrophs and their physiologies. Here we report two distinct patterns of fossilized C40 diaromatic carotenoids. Phanerozoic marine settings show distributions of diaromatic hydrocarbons dominated by isorenieratane, a biomarker derived from low-light-adapted phototrophic green sulfur bacteria. In contrast, isorenieratane is only a minor constituent within Neoproterozoic marine sediments and Phanerozoic lacustrine paleoenvironments, for which the major compounds detected are renierapurpurane and renieratane, together with some novel C39 and C38 carotenoid degradation products. This latter pattern can be traced to cyanobacteria as shown by analyses of cultured taxa and laboratory simulations of sedimentary diagenesis. The cyanobacterial carotenoid synechoxanthin, and its immediate biosynthetic precursors, contain thermally labile, aromatic carboxylic-acid functional groups, which upon hydrogenation and mild heating yield mixtures of products that closely resemble those found in the Proterozoic fossil record. The Neoproterozoic–Phanerozoic transition in fossil carotenoid patterns likely reflects a step change in the surface sulfur inventory that afforded opportunities for the expansion of phototropic sulfur bacteria in marine ecosystems. Furthermore, this expansionmight have also coincided with a major change in physiology. One possibility is that the green sulfur bacteria developed the capacity to oxidize sulfide fully to sulfate, an innovation which would have significantly increased their capacity for photosynthetic carbon fixation.

Earth's surface chemical environment has evolved from an early anoxic condition to the oxic state we have today. Transitional between an earlier Proterozoic world with widespread deep-water anoxia and a Phanerozoic world with large oxygen-utilizing animals, the Neoproterozoic Era [1000 to 542 million years ago (Ma)] plays a key role in this history. The details of Neoproterozoic Earth surface oxygenation, however, remain unclear. We report that through much of the later Neoproterozoic (<742 ± 6 Ma), anoxia remained widespread beneath the mixed layer of the oceans; deeper water masses were sometimes sulfidic but were mainly Fe²⁺-enriched. These ferruginous conditions marked a return to ocean chemistry not seen for more than one billion years of Earth history.

A quantitative mixing model coupled with new isotopic carbon data from Mongolia, northwest Canada and Namibia reveals that Neoproterozoic era carbonate isotopic anomalies can be accounted for by a primary perturbation to the surface carbon cycle, making other explanations unlikely. Uncovering the Neoproterozoic carbon cycle Stable carbon-isotope records in carbonate rocks and sedimentary organic matter give a glimpse of some of the major climatic and biological events in Earth's history. This analysis of stratigraphic sections spanning the mid-Neoproterozoic Cryogenian glacial intermission (between 717 million and 635 million years ago) in Mongolia, northern Namibia and northwestern Canada, reveals large negative isotope anomalies. The authors interpret these excursions as the consequence of a primary perturbation to the surface carbon cycle, which might reflect a series of failed transitions from the more reducing and biologically simple Proterozoic world (2,500 million to 542 million years ago) to the more oxidizing and biologically complex Phanerozoic world that we now inhabit (from 542 million years ago to the present day). Interpretations of major climatic and biological events in Earth history are, in large part, derived from the stable carbon isotope records of carbonate rocks and sedimentary organic matter 1 , 2 . Neoproterozoic carbonate records contain unusual and large negative isotopic anomalies within long periods (10–100 million years) characterized by δ 13 C in carbonate (δ 13 C carb ) enriched to more than +5 per mil. Classically, δ 13 C carb is interpreted as a metric of the relative fraction of carbon buried as organic matter in marine sediments 2 , 3 , 4 , which can be linked to oxygen accumulation through the stoichiometry of primary production 3 , 5 . If a change in the isotopic composition of marine dissolved inorganic carbon is responsible for these excursions, it is expected that records of δ 13 C carb and δ 13 C in organic carbon (δ 13 C org ) will covary, offset by the fractionation imparted by primary production 5 . The documentation of several Neoproterozoic δ 13 C carb excursions that are decoupled from δ 13 C org , however, indicates that other mechanisms 6 , 7 , 8 may account for these excursions. Here we present δ 13 C data from Mongolia, northwest Canada and Namibia that capture multiple large-amplitude (over 10 per mil) negative carbon isotope anomalies, and use these data in a new quantitative mixing model to examine the behaviour of the Neoproterozoic carbon cycle. We find that carbonate and organic carbon isotope data from Mongolia and Canada are tightly coupled through multiple δ 13 C carb excursions, quantitatively ruling out previously suggested alternative explanations, such as diagenesis 7 , 8 or the presence and terminal oxidation of a large marine dissolved organic carbon reservoir 6 . Our data from Namibia, which do not record isotopic covariance, can be explained by simple mixing with a detrital flux of organic matter. We thus interpret δ 13 C carb anomalies as recording a primary perturbation to the surface carbon cycle. This interpretation requires the revisiting of models linking drastic isotope excursions to deep ocean oxygenation and the opening of environments capable of supporting animals 9 , 10 , 11 .

The Cambrian and Ediacaran sequence of California and Nevada is rife with unconformities, paleovalleys, paleosols, and fluvial facies. This study confirms shallow marine environments for grey stromatolitic dolostone and shale of northern localities (Mt Dunfee and Westgard Pass), but fluvial red sandstones and siltstone of southern localities (Johnnie, Eagle Peak, Emigrant Pass, Donna Loy, and Cadiz) include paleosols as evidence for coastal plain and fluvial environments. Three marine transgressions into the southern localities, were in Ediacaran Johnnie Formation, earliest Cambrian Manykodes pedum zone, and Early Cambrian Olenellus trilobite zone. The southern locations have paleosols with Ediacaran fossils Ernietta , Pteridinium , Swartpuntia , and Hallidaya in growth position, as evidence that these vendobiont fossils were non marine. The paleosols include aridland Gypsids and Calcids, as well as weakly developed soils, with diagnostic LYREE enrichment, and low boron content of paleosols. Northern Ediacaran marine rocks, in contrast, are limestones with Cloudina and Wyattia , and shales with Conotubus and Wutubus . Identical marine and non-marine facies and biotas are also known from Ediacaran and Cambrian rocks of Namibia. Ediacaran marine wormlike fossils (Wormworld) were ecologically distinct and geographically separated from non-marine, sessile, vendobionts (Mattressland).

Recent geochemical data from Oman, Newfoundland, and the western United States suggest that long-term oxidation of Ediacaran oceans resulted in progressive depletion of a large dissolved organic carbon (DOC) reservoir and potentially triggered the radiation of acanthomorphic acritarchs, algae, macroscopic Ediacara organisms, and, subsequently, motile bilaterian animals. However, the hypothesized coupling between ocean oxidation and evolution is contingent on the reliability of continuous geochemical and paleontological data in individual sections and of intercontinental correlations. Here we report high-resolution geochemical data from the fossil-rich Doushantuo Formation (635-551 Ma) in South China that confirm trends from other broadly equivalent sections and highlight key features that have not been observed in most sections or have received little attention. First, samples from the lower Doushantuo Formation are characterized by remarkably stable $\\delta {}^{13}{\\rm C}{}_{\\text{org}}$ (carbon isotope composition of organic carbon) values but variable $\\delta {}^{34}{\\rm S}{}_{{\\rm CAS}}$ (sulfur isotope composition of carbonate-associated sulfate) values, which are consistent with a large isotopically buffered DOC reservoir and relatively low sulfate concentrations. Second, there are three profound negative $\\delta {}^{13}{\\rm C}{}_{\\text{carb}}$ (carbon isotope composition of carbonate) excursions in the Ediacaran Period. The negative $\\delta {}^{13}{\\rm C}{}_{\\text{carb}}$ excursions in the middle and upper Doushantuo Formation record pulsed oxidation of the deep oceanic DOC reservoir. The oxidation events appear to be coupled with eukaryote diversity in the Doushantuo basin. Comparison with other early Ediacaran basins suggests spatial heterogeneity of eukaryote distribution and redox conditions. We hypothesize that the distribution of early Ediacaran eukaryotes likely tracked redox conditions and that only after ≈551 Ma (when Ediacaran oceans were pervasively oxidized) did evolution of oxygen-requiring taxa reach global distribution.

The first animals appear during the late Ediacaran (572 to 541 Ma); an initial diversity increase was followed reduction in diversity, often interpreted as catastrophic mass extinction. We investigate Ediacaran ecosystem structure changes over this time period using the “Elements of Metacommunity Structure” framework to assess whether this diversity reduction in the Nama was likely caused by an external mass extinction, or internal metacommunity restructuring. The oldest metacommunity was characterised by taxa with wide environmental tolerances, and limited specialisation or intertaxa associations. Structuring increased in the second oldest metacommunity, with groups of taxa sharing synchronous responses to environmental gradients, aggregating into distinct communities. This pattern strengthened in the youngest metacommunity, with communities showing strong environmental segregation and depth structure. Thus, metacommunity structure increased in complexity, with increased specialisation and resulting in competitive exclusion, not a catastrophic environmental disaster, leading to diversity loss in the terminal Ediacaran. These results reveal that the complex eco-evolutionary dynamics associated with Cambrian diversification were established in the Ediacaran.