Proterozoic carbonaceous compression macrofossils are crucial for understanding the early evolution of eukaryotes. Among these, the sausage-like fossil Tawuia represents one of the earliest macro-organisms and is thus important to our understanding of the early evolution of macroscopic eukaryotes. However, its morphological evolution remains poorly understood, hampering an understanding of its taxonomy and macroevolutionary implications. Here we present a morphometric analysis of a global compilation of Tawuia specimens using pseudo-landmark-based principal component analysis. Our results reveal a distinct growth pattern of Tawuia, which nonetheless appears to have been initiated from a discoidal Chuaria-like form, confirming a close biological link between the two genera. During growth, of those specimens that became elongate, some remained straight, while others became progressively more curved. The average body size of Tawuia increased through the Proterozoic, while its morphological disparity peaked in the late Tonian, declining into the Ediacaran. We posit that elongated growth helped circumvent nutrient diffusion limitations, escape phagotrophic predation, and colonize new habitats. These results highlight the value of quantitative techniques in deciphering the early evolution of eukaryotes.

The Tonian Period represents a critical interval for the ecological rise of crown-group eukaryotes. However, our understanding of the evolutionary trajectory of early eukaryotes, particularly regarding morphological and functional innovations, remains incomplete owing to limited fossil records. In this study, we describe a new assemblage of carbonaceous compression macrofossils, comprising Chuaria, Tawuia and the 'worm-like' annulated tubular fossil Protoarenicola from the Tonian Changlingzi Formation in the Liaonan region of Liaoning Province, North China. Dark discoidal structures, which are interpreted as epibionts, were identified on the surface of these macrofossils. Biometric analysis suggests that Chuaria with a minimum diameter of no less than 1.2 mm may have a biological relationship to Tawuia. The Protoarenicola specimens, characterized by their narrow tube width and the continuous distribution of transverse annulation spacing, may represent an ecotype within the genus. This study also highlights the increasing biostratigraphic significance of annulated tubular fossils, including Protoarenicola, Pararenicola and Sinosabellidites, for global Tonian successions. Also, macroalgae may have played a significant role in promoting primary productivity and the diversification and ecological expansion of small-sized organisms.

Kimberella is an important taxon of the Ediacara biota (-574-539 million years ago), because it is one of the few with a widely accepted metazoan and even bilaterian affinity. However, this genus has very limited temporal and spatial distributions, with previously known occurrences mainly from siliciclastic rocks in the White Sea assemblage (-560-550 Ma) from Russia and South Australia. Here we report a complete Kimberella specimen and a possibly related resting trace from limestone of the terminal Ediacaran Shibantan Member (ca. 550-543 Ma), Dengying Formation, in the Yangtze Gorges area of South China. The new fossils represent one of the youngest occurrences of Kimberella, and the first record of this genus from carbonate rocks, expanding its known spatial and environmental distributions. Integrated with previously reported Dickinsonia and complex trace fossils in the same and adjacent horizons, this discovery indicates that the Shibantan biota records a pivotal evolutionary and ecological transition between the White Sea and Nama assemblages in the late Ediacaran. The Shibantan biota offers an opportunity to evaluate the evolutionary, ecological, and temporal relationship between the White Sea and Nama assemblages, to reassess the magnitude of the White Sea-Nama extinction, and to test hypotheses about the driving mechanisms responsible for the decline of the White Sea assemblage.

The emergence of eukaryotes marks a monumental juncture in the 4.6-billion-year evolutionary odyssey of our planet. Despite decades of research, the origin of eukaryotic life remains unresolved, with many of its nuances still veiled in the mists of time. While the progenitors of modern eukaryotes have roots that extend deep into the ancient past, the age of the last common ancestor to all modern eukaryotes - whether this was ancient or relatively recent - continues to spark debates. This review does not seek to settle this controversy but instead synthesizes competing perspectives from paleontology, lipid biology, molecular dating, phylogenetics, and geochemistry, emphasizing the necessity for critical evaluation of conflicting evidence across disciplines. We aim to offer a critically informed, cross-disciplinary synthesis for one of the most significant evolutionary transitions in Earth's history.

The Ediacara biota represents Earth’s earliest complex macroscopic organisms, but their biology and ecology remain poorly understood. Here we report Dengyingia pennata gen. et sp. nov., an exceptionally preserved frondose fossil from the late Ediacaran ( ~550–543 Ma) Shibantan limestone of South China. Dengyingia possesses a unique body plan: a bifoliate petalodium of unconstrained, flexible primary branches with pronounced two-sided differentiation—a smooth obverse surface and a reverse surface covered by secondary and tertiary modules. This innovation represents a key morphological advance among Ediacaran fronds. Its architecture, basal growth pattern, and suspension-feeding strategy align with those of modern sea pens (pennatulacean cnidarians), reflecting adaptations for dynamic filter-feeding in currents. Dengyingia bridges the ecological gap between the Ediacara biota and Phanerozoic suspension-feeding animals, demonstrating that complex, animal-like ecological strategies emerged before the Cambrian explosion. These findings expand Ediacaran diversity and provide insights into early animal functional differentiation. An exceptionally preserved Ediacaran frond, Dengyingia pennata, from South China shows a unique branched body plan and functional convergence with modern sea pens, suggesting complex suspension-feeding strategies evolved prior to the Cambrian diversification.

The late Ediacaran Quanjishan macrofossil assemblage of northwest China is one of the oldest fossil assemblages yet discovered in the Tibetan Plateau. It contains numerous specimens of the iconic and long-ranging soft-bodied rangeomorph Charnia, and the terminal Ediacaran candidate index fossil Shaanxilithes, preserved in siliciclastic rocks of the Zhoujieshan Formation from the Quanjishan area, northern Qaidam Basin, Tibetan Plateau. Here, we present a detailed description of Charnia fossils recently excavated from the Quanjishan assemblage, including specimens of Charnia masoni and Charnia gracilis, which are distinguished by the shape of their first-order branches and their divergence angle from the axial midline. Most Quanjishan Charnia specimens are small individuals (some are left in open nomenclature), some of which are comparable to juvenile fronds from other global Ediacaran localities, and are interpreted here as juvenile specimens. Sedimentary characteristics suggest that the Quanjishan Charnia lived in marine depositional environments somewhere between shoreface and offshore transition, and under low-to-moderate energy hydrodynamic conditions, which supports the suggestion that Charnia preferred calmer habitats. Three-dimensional preservation exhibiting both surfaces of the frondose fossils is recognized in the Quanjishan assemblage, providing a new taphonomic window into three-dimensional preservation of Ediacaran soft-bodied organisms. The Quanjishan assemblage extends the palaeogeographic distribution of Charnia as well as rangeomorphs, and emphasizes that Charnia is one of the longest-ranging genera among the Ediacaran macrobiota.

The emergence of land plants was a pivotal development in Earth history. It has been postulated that the evolutionary transition from freshwater streptophyte algae to land plants, or the canalization of plant meiosis, was completed during the Middle Ordovician ( 460 Ma). However, the absence of undisputed streptophyte algal fossils (for example, Charophyceae) earlier than the late Silurian ( 425 Ma) has obscured this link between streptophyte algae and land plants. Here we describe a marine Charophyceae fossil, Tarimochara miraclensis gen. et sp. nov., from early and middle Katian (Late Ordovician, 453–449 Ma) marine limestones in northwestern China. This discovery demonstrates that at least some species of Charophyceae inhabited shallow normal marine environments at that time. Moreover, these early Charophyceae show that some key morphological innovations associated with an evolutionary transition between streptophyte algae and land plants had occurred before the early Katian. This provides crucial evidence relevant to the origins of land plants. Land plants diverged from streptophyte algae around 460 million years ago. Marine Charophyceae fossils from the Upper Ordovician confirm that morphological innovations key to the evolution of terrestrial flora predate the emergence of land plants.

Pre-Cryogenian organic-walled microfossils with delicate cellular preservation can provide pivotal information for the origin and early evolution of multicellular eukaryotes. With previously reported evidence for true dichotomous branching and photosynthesis, the filamentous fossil Arctacellularia is among one of the few examples of pre-Cryogenian unambiguous multicellular algae. However, the taxonomic diversity of this genus has remained controversial for decades, and its evolutionary implications for understanding the emergence and maintenance of filamentous multicellularity and branching in eukaryotes have been underexplored. Here, we report well-preserved Arctacellularia fossils extracted from the drill core samples of the early Tonian Liulaobei Formation (similar to 0.95-0.92 Ga), Huainan region, northern Anhui Province, North China. Two species have been recognized in the Liulaobei Formation, including the type species Arctacellularia tetragonala, with one trichome showing evidence of a possible nodal cell indicative of branching, and Arctacellularia ellipsoidea, distinguished by the presence/absence of barrel-like to long cylindrical cells (with a length/width ratio >= 1.5). Arctacellularia is reconstructed as a uniserial multicellular filamentous organism enveloped by common membrane in this study; it consists of three types of possibly differentiated cells that are characterized by terminal folds (or terminal extensions), and can occasionally bifurcate once via a nodal cell. This study suggests that the maintenance of filamentous multicellularity of Arctacellularia is achieved by a combination of common membrane, terminal folds, and siphonous construction. Furthermore, the dichotomous branching of Arctacellularia appears morphologically more primitive than those observed in other Pre-Cryogenian fossils, including Cheilofilum, Jacutianema, and Proterocladus. Given that Arctacellularia has been phylogenetically placed in the total group of Archaeplastida and the oldest Arctacellularia specimens date back to similar to 1.7-1.4 Ga, if the early Mesoproterozoic material is confirmed to be biologically congeneric with the early Tonian counterpart, it suggests that Archaeplastida may have acquired multicellularity, siphonous construction, cellular differentiation, and possibly branching at least 1.4 billion years ago.

The Tonian Period (1000–720 Ma) bore witness to the transition from a prokaryote-dominated marine ecosystem to one characterized by the proliferation of eukaryotes. This fundamental shift has generally been attributed to evolving marine redox states. Here, we present sedimentological and geochemical analyses of the early Tonian Huainan, Feishui, and Huaibei groups in the Xuhuai basin of the North China craton. Multiple redox proxies show consistent, water depth-dependent variations across the Xuhuai basin. Excess barium contents and Ba/Al ratios further highlight spatial variations in primary productivity which ultimately regulate basinal redox structures. We propose that a shallow-water oxygen minimum zone sandwiched between the oxic/suboxic mid-depth and surface layer water masses occur in the oligotrophic Xuhuai basin, which is analogous to, but much shallower than modern oxygen minimum zones. Such marine redox architectures may benefit the maintenance of a bioavailable nitrate reservoir in the ocean, foreboding the subsequent expansion of eukaryotes. A shallow-water anoxic zone sandwiched between the oxic surface layer and mid-depth water masses occurs in the oligotrophic early Tonian Xuhuai basin of North China craton. It is analogous to, but much shallower than, modern oxygen minimum zones.

The terminal Ediacaran Shibantan biota (~550–543 Ma) from the Dengying Formation in the Yangtze Gorges area of South China represents one of the rare examples of carbonate-hosted Ediacara-type macrofossil assemblages. In addition to the numerically dominant taxa—the non-biomineralizing tubular fossil Wutubus and discoidal fossils Aspidella and Hiemalora , the Shibantan biota also bears a moderate diversity of frondose fossils, including Pteridinium , Rangea , Arborea , and Charnia . In this paper, we report two species of the rangeomorph genus Charnia , including the type species Charnia masoni Ford, 1958 emend. and Charnia gracilis new species, from the Shibantan biota. Most of the Shibantan Charnia specimens preserve only the petalodium, with a few bearing the holdfast and stem. Despite overall architectural similarities to other Charnia species, the Shibantan specimens of Charnia gracilis n. sp. are distinct in their relatively straight, slender, and more acutely angled first-order branches. They also show evidence that may support a two-stage growth model and a epibenthic sessile lifestyle. Charnia fossils described herein represent one of the youngest occurrences of this genus and extend its paleogeographic and stratigraphic distributions. Our discovery also highlights the notable diversity of the Shibantan biota, which contains examples of a wide range of Ediacaran morphogroups. UUID: http://zoobank.org/837216cd-4a4a-4e13-89e2-ee354ba48a4c

Longfengshania is among the few examples of Pre-Cryogenian macroscopic fossils with an unambiguous eukaryotic affinity. It has received great attention since this genus is the earliest known Pre-Cryogenian macroalga with blade, stipe, and holdfast differentiation. However, compared to other macrofossils, such as Chuaria and Tawuia, reported occurrences (lithostratigraphic units) of Longfengshania are limited in Tonian strata, restricting the assessment of paleogeographic distribution of Longfengshania and therefore hindering our understanding of its paleoecological role in the Tonian oceans. Here, we describe two new localities of Longfengshania, including the Tonian Shiwangzhuang Formation (similar to 850-720 Ma) in western Shandong and Jiuliqiao Formation (similar to 950-720 Ma) in northern Anhui, North China. Specimens of Longfengshania from the Shiwangzhuang and Jiuliqiao formations are smaller than specimens from other localities, which has been interpreted as adaptations to relatively stronger hydrodynamic conditions. Biometric and principal component analyses suggest that most other species of Longfengshania actually fall within the morphospace range of the type species L. stipitata and therefore a re-examination on previously reported specimens and a taxonomic revision for this genus are needed in future study. (c) 2023 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Early to middle Ediacaran organic-rich black shales host several famous fossil biotas and provide key evidence for understanding the coevolution of multicellular organisms and palaeoceanic environment. The water column redox states play critical roles in organic-rich shale deposition. Amongst multiple geochemical redox indexes, iron-speciation chemistry (FeHR/FeT, Fepy/FeHR) in shales constitutes a reliable proxy to reconstruct the first-order redox framework of the ocean basin. However, iron-speciation is a local marine redox proxy, and only compiled data collected from multiple different sedimentary facies record statistically significant changes of oxidation states within a depositional basin. Here we compiled the spatiotemporal distribution of iron-speciation data in early to middle Ediacaran black shales of the Yangtze block in South China. New high-resolution analysis on two outcrops and one drill-core reflects overall ferruginous condition and dominant euxinic condition locally interrupted by oxic states, respectively, generally indicating pervasive anoxic depositional environment for the Member II shales of the Ediacaran Doushantuo Formation in the Lower Yangtze block. Compilation of fourteen Ediacaran sections from shallow-, slope- and deep-water facies demonstrates frequent spatiotemporal oscillation of the redox conditions throughout the Yangtze block. Widespread ferruginous states, accompanied with euxinic zones mainly focusing in lower slope facies, are detected during the early Ediacaran period, in contrast with more widespread euxinic settings in the middle Ediacaran period. Statistical data including new high-resolution results from the Lower Yangtze block show generally low enrichment for redox sensitive elements (RSEs, e.g., Mo, V and U) in the Member II shales probably due to their contemporary low seawater concentrations. An increase of RSEs concentrations occurs in the Member IV shales, which probably reflects more oxidized Earth surface environment during middle Ediacaran period. The increasing Earth oxygenation documents the occurrence of widespread euxinic states during deposition of the Member IV shales. Compilation of spatial distribution of TOC contents in black shales demonstrates their apparent relevance to spatial distribution of the euxinic rather than ferruginous states, which is likely due to the favorable role of sulfurization process on burial and preservation of organic matters. The euxinic states may also facilitate the exceptional preservation of the soft-bodied Ediacaran fossils.

The global diversity of Proterozoic eukaryote fossils is poorly quantified despite its fundamental importance to the understanding of macroevolutionary patterns and dynamics on the early Earth. Here we report a new construction of fossil eukaryote diversity from the Paleoproterozoic to early Cambrian based on a comprehensive data compilation and quantitative analyses. The resulting taxonomic richness curve verifies Cryogenian glaciations as a major divide that separates the “Boring Billion” and Ediacaran periods, with the former characterized by a prolonged stasis, and the latter by greater diversity, more-rapid turnover, and multiple radiations and extinctions. These contrasting evolutionary patterns and dynamics provide a framework to test competing hypotheses on biosphere and geosphere coevolution in the Proterozoic Eon.

Sponges are the most basal metazoan phylum1 and may have played important roles in modulating the redox architecture of Neoproterozoic oceans2. Although molecular clocks predict that sponges diverged in the Neoproterozoic era3,4, their fossils have not been unequivocally demonstrated before the Cambrian period5-8, possibly because Precambrian sponges were aspiculate and non-biomineralized9. Here we describe a late-Ediacaran fossil, Helicolocellus cantori gen. et sp. nov., from the Dengying Formation (around 551-539 million years ago) of South China. This fossil is reconstructed as a large, stemmed benthic organism with a goblet-shaped body more than 0.4 m in height, with a body wall consisting of at least three orders of nested grids defined by quadrate fields, resembling a Cantor dust fractal pattern. The resulting lattice is interpreted as an organic skeleton comprising orthogonally arranged cruciform elements, architecturally similar to some hexactinellid sponges, although the latter are built with biomineralized spicules. A Bayesian phylogenetic analysis resolves H. cantori as a crown-group sponge related to the Hexactinellida. H. cantori confirms that sponges diverged and existed in the Precambrian as non-biomineralizing animals with an organic skeleton. Considering that siliceous biomineralization may have evolved independently among sponge classes10-13, we question the validity of biomineralized spicules as a necessary criterion for the identification of Precambrian sponge fossils.

Evaporites are climate-sensitive sedimentary deposits with event stratigraphic, paleogeographic, and paleoenvironmental significance. The Early Cambrian is characterized by early evolution of animal and extensive evaporite deposits at the end. Widespread evaporite deposits were developed in the lower Cambrian succession in the North China Craton (NCC), which could provide critical constraints on the age of evaporite-bearing strata, the reconstruction of paleogeographic evolution, and the paleoenvironmental change of the NCC during the Early Cambrian. In this study, we systematically synthesized the geographical and stratigraphic distributions of the Early Cambrian evaporite deposits in the NCC based on field collections and published data. The results show that the Early Cambrian evaporite deposits in the NCC mainly include gypsum, halite pseudomorph, and gypsum breccia. They have been found in two sets of reddish layers and geographically distributed in the Jiao-Liao-XuHuai region and western Henan region. Integrated evidence of biostratigraphy, chemostratigraphy, and detrital zircon chronology constrains the age of these evaporite deposits within the Cambrian Series 2, Stage 4 (ca. 514-509 Ma). Consequently, these late Early Cambrian evaporite deposits represent drought events that can act as regional event stratigraphic markers to constrain the age of the evaporite-bearing strata near the Great Unconformity and also suggest that the paleogeographic position of the NCC in the Cambrian Stage 4 may be located between 20 degrees N-30 degrees N near the western Gondwana with northwest-southeast orientation. Additionally, the hot-arid paleoclimate evidenced by evaporite deposits may be the environmental factors for the decline of benthic organisms in the NCC in the late Early Cambrian.

The Great Unconformity at the Precambrian-Cambrian boundary has been recognized on several continents and may provide critical insights into the environmental context of the Cambrian explosion. However, the geodynamic drivers, geochronological duration, and paleogeographic extent of the Great Unconformity remain unconstrained in many cases. Recently, a major depositional gap of varying magnitudes has been reported around the Precambrian-Cambrian boundary in several regions of North China, leading to the interpretation that the Great Unconformity may have been widespread but diachronous across the North China Craton. However, the magnitude of the Great Unconformity remains unknown in northeastern North China, largely because of the poor age constraints on the thick Proterozoic-Cambrian successions in this region. Here we use biostratigraphic data to constrain the depositional age of Proterozoic strata below the Great Unconformity in northeastern North China. We report a diverse organic-walled microfossil assemblage from the Qinggouzi Formation in southern Jilin Province, northeastern margin of the North China Craton. Typical late Mesoproterozoic to early Neoproterozoic microfossils, including Trachyhystrichosphaera aimika and Proterocladus antiquus, are present in Qinggouzi assemblage, providing a solid biostratigraphic constraint on the Qinggouzi Formation. Given that the overlying Shuidong Formation contains typical early Cambrian small shelly fossils, our new data indicate that the Great Unconformity in northeastern North China represents a major depositional gap of >200 Myr. Thus, the new data, along with other available biostratigraphic and geochronological data from over the world, provide robust constraints on the paleogeographic extent, chronostratigraphic duration, and diachronous nature of the Great Unconformity.