Shuhai Xiao

Virginia Tech (Virginia Polytechnic Institute and State University) | VT · Department of Geosciences

Cloudina is the best-known biomineralizing metazoan and a potential index fossil in the late Ediacaran Period, yet many aspects of its biology remain poorly understood. Previous reports have shown that Cloudina tubes grow from a basally closed funnel (or apical element), with occasional dichotomous branching. New material from the Ediacaran Beiwan...

Morphological phylogenetic analyses suggest that scalidophorans (priapulids, loriciferans, and kinorhynchs) and nematoids (nematodes and nematomorphs) form the ecdysozoan clade Cycloneuralia, which is a sister group to panarthropods. It has been proposed that extant priapulids and Cambrian priapulid-like scalidophorans, because of their conserved e...

Ediacara fossils are central to our understanding of animal evolution on the eve of the Cambrian explosion, because some of them likely represent stem-group marine animals. However, some of the iconic Ediacara fossils have also been interpreted as terrestrial lichens or microbial colonies. Our ability to test these hypotheses is limited by a taphon...

Some of the enigmatic Precambrian organisms in the Ediacaran Period grew large and stood tall above the seafloor. Canopy flow modeling suggests that their large size was optimized for access to flow in order to facilitate osmotrophic nutrient uptake in low-flow environments.

Earth’s magnetic field was in a highly unusual state when macroscopic animals of the Ediacara Fauna diversified and thrived. Any connection between these events is tantalizing but unclear. Here, we present single crystal paleointensity data from 2054 and 591 Ma pyroxenites and gabbros that define a dramatic intensity decline, from a strong Proteroz...

This work presents a detailed taxonomic study on organic-walled microfossils from the Ediacaran Sete Lagoas Formation (Bambuí Group) at the Barreiro section in the Januária area of the São Francisco basin, Brazil. Seven species are described, including Siphonophycus robustum (Schopf, 1968), Ghoshia januarensis new species, Leiosphaeridia crassa (Na...

Brown algae are the only group of heterokont protists exhibiting complex multicellularity. Since their origin, brown algae have adapted to various marine habitats, evolving diverse thallus morphologies and gamete types. However, the evolutionary processes behind these transitions remain unclear due to a lack of a robust phylogenetic framework and p...

Sedimentary pyrite has long been used as an archive of marine environments in Earth history. To capture reliable paleoenvironmental signals, however, we need to first evaluate pyrite in sedimentary strata as it can be altered and masked by later diagenetic and/or hydrothermal processes. Here, we trained two supervised machine learning algorithms on...

Cycloneuralians are ecdysozoans with a fossil record extending to the Early Cambrian Fortunian Age and represented mostly by cuticular integuments. However, internal anatomies of Fortunian cycloneuralians are virtually unknown, hampering our understanding of their functional morphology and phylogenetic relationships. Here we report the exceptional...

The Viridiplantae comprise two main clades, the Chlorophyta (including a diverse array of marine and freshwater green algae) and the Streptophyta (consisting of the freshwater charophytes and the land plants). Lineages sister to core Chlorophyta, informally refer to as prasinophytes, form a grade of mainly planktonic green algae. Recently, one of t...

The Snowball Earth hypothesis predicts that continental chemical weathering was curtailed substantially during but rebounded strongly after the Marinoan ice age some 635 million years ago. Defrosting the planet would result in a plume of fresh glacial meltwater with a different chemical composition than underlying hypersaline seawater, generating a...

The Ediacaran Period (~635–539 Ma) is marked by the emergence and diversification of complex metazoans linked to ocean redox changes, but the processes and mechanism of the redox evolution in the Ediacaran ocean are intensely debated. Here we use mercury isotope compositions from multiple black shale sections of the Doushantuo Formation in South Ch...

Microbially induced sedimentary structures (MISS) are abundant in Ediacaran and lower Cambrian successions. However, the relationship between MISS distribution and facies has not been thoroughly explored in Ediacaran–Cambrian successions in South America. This study documents the occurrence of MISS and other potential biogenic structures from the l...

Macrofossils with unambiguous biogenic origin and predating the one-billion-year-old mul-ticellular fossils Bangiomorpha and Proterocladus interpreted as crown-group eukaryotes are quite rare. Horodyskia is one of these few macrofossils, and it extends from the early Mesoproterozoic Era to the terminal Ediacaran Period. The biological interpretatio...

During the Marinoan Ice Age (ca. 654–635 Ma), one of the ‘Snowball Earth’ events in the Cryogenian Period, continental icesheets reached the tropical oceans. Oceanic refugia must have existed for aerobic marine eukaryotes to survive this event, as evidenced by benthic phototrophic macroalgae of the Songluo Biota preserved in black shales interbedde...

Humans have made profound changes to the Earth. The resulting societal challenges of the Anthropocene (e.g., climate change and impacts, renewable energy, adaptive infrastructure, disasters, pandemics, food insecurity, and biodiversity loss) are complex and systemic, with causes, interactions, and consequences that cascade across a globally connect...

The early Neoproterozoic Era witnessed the initial ecological rise of eukaryotes at ca. 800 Ma. To assess whether nitrate availability played an important role in this evolutionary event, we measured nitrogen isotope compositions (δ15N) of marine carbonates from the early Tonian (ca. 1000 Ma to ca. 800 Ma) Huaibei Group in North China. The data rep...

The Ediacaran-Cambrian transition interval is described for the west part of the Gond-wana Supercontinent. This key interval in Earth's history is recorded in the upper and lower part of the Tagatiya Guazú and Cerro Curuzu formations, Itapucumi Group, Para-guay, encompassing a sedimentary succession deposited in a tidally influenced mixed carbonate...

Proterozoic eukaryotic macroalgae are difficult to interpret because morphological details required for proper phylogenetic studies are rarely preserved. This is especially true of morphologically simple organisms consisting of tubes, ribbons, or spheres that are commonly found in a wide array of bacteria, plants, and even animals. Previous reports...

The upper Ediacaran Miaohe Member (~550 Ma) in South China is well known for exceptionally preserved macroscopic carbonaceous compression fossils (i.e., the Miaohe biota) that are pivotal in understanding the marine ecology and environment during the terminal Ediacaran Period. However, micro-organisms, which are also important biotic components of...

Complex multicellular eukaryotic organisms (or “complex organisms”), including animals, land plants, fungi, and macroalgae, have dominated the Earth’s biosphere since the Precambrian-Cambrian transition. Although fossil evidence and molecular clock estimates indicate that the early adaptive radiation of complex organisms occurred no later than the...

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 Hiem...

Systematic extinctions can leave major morphological gaps between living crown‐group clades. Such morphological gaps would be perceived, from a neontological point of view, as major evolutionary transitions. In order to fill these morphological gaps and to map the evolutionary steps toward major evolutionary transitions, we need to integrate extinc...

The Ediacara Biota-the oldest communities of complex, macroscopic fossils-consists of three temporally distinct assemblages: the Avalon (ca. 575-560 Ma), White Sea (ca. 560-550 Ma), and Nama (ca. 550-539 Ma). Generic diversity varies among assemblages, with a notable decline at the transition from White Sea to Nama. Preservation and sampling biases...

The early history of deuterostomes, the group composed of the chordates, echinoderms and hemichordates1, is still controversial, not least because of a paucity of stem representatives of these clades2–5. The early Cambrian microscopic animal Saccorhytus coronarius was interpreted as an early deuterostome on the basis of purported pharyngeal opening...

The Ediacaran Doushantuo Formation in South China documents profound biological and environmental changes after the Neoproterozoic global glaciations. However, since the geological records of these changes are scattered in various lithofacies, the establishment of the co-evolutionary pattern of life and environment largely relies on regional strati...

Microfossils of the Ediacaran Doushantuo Formation in South China provide an important window onto the rapid diversification of marine eukaryotes after the terminal Cryogenian global glaciation. They also offer key data in the biostratigraphic subdivision and correlation of the lower–middle Ediacaran System. Previously published Doushantuo microfos...

The Ediacaran Shuram excursion (SE) records a global decrease in carbonate carbon isotope (δ¹³Ccarb) values from +6‰ down to ca. –10‰, representing the largest δ¹³Ccarb negative anomaly in Earth history. While the SE is widely recorded in the upper Doushantuo Formation of South China, it shows highly variable δ¹³Ccarb profiles among correlative sec...

Glacial diamictites of the Cryogenian Nantuo Formation of the Yangtze Craton of South China record major environmental transitions during the Marinoan glaciation. Although the provenance of the siliciclastic materials in the Nantuo Formation have been constrained via detrital zircon analysis, the source areas for the abundant carbonate clasts withi...

Cryogenian snowball Earth glaciations may have had disastrous impacts on the biosphere, particularly the terrestrial ecosystem. However, how the terrestrial ecosystem responded to and recovered from these glaciations remains poorly understood. Speleothems offer important insights into terrestrial life because their formation is critically dependent...

Microbially induced sedimentary structures (MISS) are abundant in Ediacaran and lower Cambrian successions. However, the relationship between MISS distribution and facies has not been thoroughly studied, particularly in successions of this time interval in South America. In this study, we document the occurrence of MISS and other potential biogenic...

Trace fossils record foraging behaviors, the search for resources in patchy environments, of animals in the rock record. Quantification of the strength, density, and nature of foraging behaviors enables the investigation of how these may have changed through time. Here, we present a novel approach to explore such patterns using spatial point proces...

Cryogenian snowball Earth glaciations may have had disastrous impacts on the biosphere, particularly the terrestrial ecosystem. However, how the terrestrial ecosystem responded to and recovered from these glaciations remains poorly understood. Speleothems offer important insights into terrestrial life because their formation is critically dependent...

Significance Earth system’s response to major perturbations is of paramount interest. On the basis of multiple isotope compositions for pyrite, carbonate-associated sulfate, carbonates, and organics within, we inferred that the much-debated, enigmatic, extremely ¹³ C-depleted calcite cements in the ∼635-Ma cap carbonates in South China preserve geo...

The rise of eukaryotic macroalgae in the late Mesoproterozoic to early Neoproterozoic was a critical development in Earth’s history that triggered dramatic changes in biogeochemical cycles and benthic habitats, ultimately resulting in ecosystems habitable to animals. However, evidence of the diversification and expansion of macroalgae is limited by...

Acritarch biostratigraphic and δ ¹³ C chemostratigraphic data from the Krol A Formation in the Solan area (Lesser Himalaya, northern India) are integrated to aid inter-basinal correlation of early–middle Ediacaran strata. We identified a prominent negative δ ¹³ C excursion (likely equivalent to EN2 in the lower Doushantuo Formation in the Yangtze G...

The Earth's redox evolution has been commonly assumed to have played a key role in shaping the evolutionary history of the biosphere. However, whether and how shifts in marine redox conditions are linked to key biotic events – foremost the rise of animals and the ecological expansion of eukaryotic algae in the late Proterozoic oceans – remains heav...

The Ulvophyceae, a major group of green algae, is of particular evolutionary interest because of its remarkable morphological and ecological diversity. Its phylogenetic relationships and diversification timeline, however, are still not fully resolved. In this study, using an extensive nuclear gene dataset, we apply coalescent- and concatenation-bas...

Compared with Phanerozoic strata, sulfate minerals are relatively rare in the Precambrian record likely due to the lower concentrations of sulfate in dominantly anoxic oceans. Here, we present a compilation of sulfate minerals that are stratigraphically associated with the Ediacaran Shuram excursion (SE) — the largest negative δ ¹³ C excursion in E...

The Tonian Period witnessed important environmental changes and critical evolutionary innovations. Published iron speciation data suggest a global redox transition of mid‐depth seawaters from euxinic to ferruginous in early Tonian, but details of this transition remain unknown. This study explores Tonian stromatolitic carbonates as a possible archi...

Since the report of tubular structures interpreted as Cloudina from the Neoproterozoic Sete Lagoas Formation (SLF) in the Bambuí basin of eastern Brazil, this stratigraphic unit has become a focus of numerous geochemical, paleomagnetic, geochronological and sequence stratigraphic studies. Geochemical data from the SLF have been used to infer paleoe...

Abstract can be found at http://dx.doi.org/10.46427/gold2022.8849

Red to red-orange spheres in the vascular canals of fossil bone thin sections have been repeatedly reported using light microscopy. Some of these have been interpreted as the fossilized remains of blood cells or, alternatively, pyrite framboids. Here, we assess claims of blood cell preservation within bones of the therizinosauroid theropod Beipiaos...

Dickinsonia is an iconic fossil of the Ediacara biota (∼575–539 Ma). It was previously known from siliciclastic successions of the White Sea assemblage in Australia, Baltica, and possibly India. Here we describe Dickinsonia sp. from the terminal Ediacaran Shibantan Member limestone (ca. 551–543 Ma) of the Dengying Formation in the Yangtze Gorges ar...

Compared with the Phanerozoic strata, sulfate minerals are notably rare in the Precambrian record largely due to lower concentrations of sulfate in dominantly anoxic oceans. Here, we present a compilation of sulfate minerals, including diagenetic barite (BaSO4), pseudomorphs of gypsum (CaSO4·2H2O) and anhydrite (CaSO4), and celestine (SrSO4) that a...

The Ediacaran Period (ca. 635-539 Ma) witnessed the earliest paleontological evidence for macroscopic life (i.e., Ediacara biota) and geochemical observations of the largest carbon cycle J o u r n a l P r e-p r o o f Journal Pre-proof anomaly in Earth history (i.e., Shuram Excursion, SE). Numerous hypotheses have been proposed for the origins of th...

The largest carbon isotope (δ13C) negative anomaly recorded in marine carbonates in Earth history — the Ediacaran Shuram Excursion (SE) — preserves values down to ca. –10‰ on a global scale. Despite the intensive geochemical and theoretical work published in the past decade, its origin and the degree to which its geochemical signature has been diag...

The geological time scale before 720 Ma uses rounded absolute ages rather than specific events recorded in rocks to subdivide time. This has led increasingly to mismatches between subdivisions and the features for which they were named. Here we review the formal processes that led to the current time scale, outline rock-based concepts that could be...

Symbiosis represents close and long-term interactions—which can be mutualistic, commensalistic, or parasitic—between two different taxa. Symbiotic associations play a pivotal role in accelerating eukaryotic evolution and diversification. However, the Proterozoic fossil record of symbiosis is rarely documented despite the abundance of Proterozoic eu...

Proterozoic carbonaceous macrofossils are key to understand the evolution of early eukaryotes and how they acquired macroscopic sizes. However, phylogenetic interpretation of these macrofossils is challenging because most of them are morphologically simple and lack phylogenetically diagnostic features. Among Proterozoic carbonaceous macrofossils, t...

Molecular phylogenetic data suggest that photosynthetic eukaryotes first evolved in freshwater environments in the early Proterozoic and diversified into marine environments by the Tonian Period, but early algal evolution is poorly reflected in the fossil record. Here, we report newly discovered, millimeter- to centimeter-scale macrofossils from ou...

The global deposition of superheavy pyrite (pyrite isotopically heavier than coeval seawater sulfate in the Neoproterozoic Era and particularly in the Cryogenian Period) defies explanation using the canonical marine sulfur cycle system. Here we report petrographic and sulfur isotopic data (δ34Spy) of superheavy pyrite from the Cryogenian Datangpo F...

Annulated discoidal structures are common in many Neoproterozoic and particularly Ediacaran successions. Their interpretations, especially their biogenicity, are often contentious. Some of them (e.g., Aspidella and related forms) are demonstrably biological structures and may represent holdfasts of frondose Ediacara-type organisms. Others may repre...

The colonization of land by fungi had a significant impact on the terrestrial ecosystem and biogeochemical cycles on Earth surface systems. Although fungi may have diverged ~1500–900 million years ago (Ma) or even as early as 2400 Ma, it is uncertain when fungi first colonized the land. Here we report pyritized fungus-like microfossils preserved in...

The advent of biomineralizing metazoans in the terminal Ediacaran Age (ca. 550–539 Ma) represents a remarkable biological innovation in the history of life. As a poster child of this evolutionary episode, Cloudina is widely regarded as a weakly biomineralizing tubular fossil with a global distribution. Therefore, Cloudina can both inform the evolut...

As part of the most common eukaryotic fossils in early Ediacaran strata, acanthomorphic acritarchs are crucial for understanding the biostratigraphy and evolutionary dynamics of marine eukaryotes after the Marinoan global glaciation. Abundant and diverse acanthomorphic acritarchs have been reported from the Ediacaran Doushantuo Formation in the Yan...

Four first-order (Hadean, Archean, Proterozoic and Phanerozoic eon) and nine second-order (Paleoarchean, Mesoarchean, Neoarchean, Paleoproterozoic, Mesoproterozoic, Neoproterozoic, Paleozoic, Mesozoic and Cenozoic era) units continue to provide intuitive subdivision of geological time. Major transitions in Earth’s tectonic, biological and environme...

The Shibantan Lagerstätte (551-543 Ma) in the Yangtse Gorges area in South China is one of the best-known examples of terminal Ediacaran fossil assemblages preserved in marine carbonate rocks. Taxonomically dominated by benthic organisms, the Shibantan Lagerstätte preserves various photoautotrophs, biomineralizing tubular fossils, Ediacara-type mac...

The ecdysozoans are the most diverse animal group on Earth 1, 2 . Molecular clock studies indicate that the ecdysozoans may have diverged and diversified in the Ediacaran Period 3, 4 , but unambiguous ecdysozoan fossils first appear in the earliest Cambrian and are limited to cycloneuralians 5–7 . Here we report new material of the early Cambrian m...

The Ediacara biota records the rise of morphologically complex macroscopic eukaryotes, including animals and other heterotrophs. Eltonian ecology demands that Ediacaran ecosystems must have been supported by primary producers (e.g., cyanobacteria, phytoplanktonic eukaryotes, benthic macroalgae). But the fossil record of Ediacaran primary producers...

Ediacaran phosphorites capture the dynamics of the ultimate biolimiting nutrient, phosphorus, during perhaps the most critical transition of Earth's climatic and ecological history. Concomitant with the Neoproterozoic Oxygenation Event was the deposition of the first extensive phosphorites across marine shelves, typically interpreted as a basinward...

Bituminous limestone of the Ediacaran Shibantan Member of the Dengying Formation (551–539 Ma) in the Yangtze Gorges area contains a rare carbonate-hosted Ediacara-type macrofossil assemblage. This assemblage is dominated by the tubular fossil Wutubus Chen et al., 2014 and discoidal fossils, e.g., Hiemalora Fedonkin, 1982 and Aspidella Billings, 187...

Benthic marine macroalgae or seaweeds are key ecological players in oceans today and have been since the Proterozoic. To date, however, morphological and evolutionary patterns for Precambrian macroalgae have been documented only in rather broad terms. To refine our understanding in this critical interval, we updated a dataset of Proterozoic to earl...

The broad-scale environment plays a substantial role in shaping modern marine ecosystems, but the degree to which palaeocommunities were influenced by their environment is unclear. To investigate how broad-scale environment influenced the community ecology of early animal ecosystems, we employed spatial point process analyses (SPPA) to examine the...

Raman spectroscopy is a minimally intrusive and minimally destructive technique that has played an important role in analyzing Precambrian carbonaceous microfossils and microstructures. Previous studies have shown that heterogeneities in structural order of carbonaceous material (CM) as revealed by Raman spectroscopy can be preserved in Proterozoic...

Ediacaran macrofossils are typically preserved in three taphonomic modes: casts/molds in siliciclastic rocks, casts/molds in carbonate rocks, and carbonaceous compressions in black shales. Only a few taxa are known to be preserved in more than one of these taphonomic modes. Flabellophyton is a genus that has been previously reported from lower Edia...

Most Precambrian sediment-hosted barites have been interpreted to be diagenetic, hydrothermal exhalation, or methane-seepage in origin. Seafloor barite precipitates and void-filling barite cements in basal Ediacaran cap dolostones have been interpreted as sedimentary and early diagenetic in origin, and they have been used to infer ocean geochemistr...

Chlorophytes (representing a clade within the Viridiplantae and a sister group of the Streptophyta) probably dominated marine export bioproductivity and played a key role in facilitating ecosystem complexity before the Mesozoic diversification of phototrophic eukaryotes such as diatoms, coccolithophorans and dinoflagellates. Molecular clock and bio...

Zhou et al. (2004) reported a zircon U-Pb isotope dilution - thermal ionization mass spectrometry (ID-TIMS) age of 662.9 ± 4.3 Ma from the basal Datangpo Formation of the Cryogenian System in South China. It was the first zircon U-Pb age to constrain both the termination of Sturtian glaciation and the onset of Marinoan glaciation, despite its much...