Oceanic anoxic events (OAEs) are commonly linked to global drivers, but the role of basin configuration and tectonic instability in sustaining long-lived anoxic conditions remains insufficiently understood. In Baltoscandia, the Miaolingian–Tremadocian Alum Shale Formation (~ 513–484 Ma) records the regionally restricted Alum Oceanic Anoxic Episode (AOAE), which persisted for ~30 Myr and led to the accumulation of kerogenous black shales. This updated review integrates stratigraphic, palaeontological, sedimentological, and geochemical evidence to assess the environmental and tectonic controls on basin circulation and redox conditions during the AOAE. Deposition occurred in a semi-enclosed, flat-floored epicontinental basin developed largely on the Transscandinavian Igneous basement. Restricted circulation, high productivity, and persistent water-column stratification promoted dysoxic to anoxic bottom-water conditions, favouring exceptional preservation of organic matter and enrichment in pyrite and redox-sensitive elements. The succession is punctuated by breccias, conglomerates, shelly limestones, karstic surfaces, synsedimentary faults and Neptunian dykes, recording recurrent tectonic pulses involving local uplift and tilting. These events intermittently modified basin geometry and circulation patterns, facilitating short-term oxygenation episodes, carbonate and phosphogenic production, and localized hydrothermal activity associated with polymetallic mineralization. The AOAE started following renewed transgression after the ‘Hawke Bay unconformity’, and ended with a major uplift and regression recorded by the Bjørkåsholmen Formation, both likely related to Caledonian tectonic activity. The Alum Shale Formation provides an exceptional example of how persistent anoxia can be sustained in a semi-restricted epicontinental basin through the interplay of palaeogeographic confinement, episodic tectonic, hydrothermal fluxes, and water-column stratification, largely independent of globally synchronous OAEs.

The lingulide brachiopod Mergliella sp. aff. M. bechei, with an exceptionally preserved three-dimensional pedicle, is described from the upper part of the Cae'r mynach Formation (Silurian, late Ludfordian) in Wales, UK, where it occurs with a limited shelly fauna and fine plant debris. The shells of Mergliella were probably exhumed locally by a thin storm sand sheet reaching into a subtidal delta-front environment and were transported little. Microbial mats developing in the fairweather environment, limited bioturbation and a sparse shelly fauna suggest an anachronistic taphonomic environment where the soft tissue became preserved. Fossilisation in dysaerobic or euxinic conditions resulted in replacement of organic tissues by platelets of clay minerals and fine pyrite crystal growth around the shell. Soft tissue preservation in this taphonomic environment is rare in shallow subtidal environments after Proterozoic-early Cambrian times except after ecosystem disruption such as extinction events. This is the only example of soft tissue preservation in a linguliform brachiopod from the Silurian Period. square Lagerst & auml;tte preservation, Brachiopoda, Lingulida, Silurian, Wales, taphonomy.

The Brachiopoda were one of the most successful groups of marine invertebrates during the Palaeozoic Era, exhibiting exceptional diversity and abundance. Linguloid brachiopods (superfamily Linguloidea), initially characterized by an epibenthic mode of life in the Cambrian, underwent substantial diversification during the Ordovician, including the emergence of infaunal forms. This interval marks the peak of their morphospace occupation and ecological diversification. To gain a deeper understanding of the ecological evolution of linguloid brachiopods, a comprehensive investigation of their morphological and anatomical evolution is essential. Here, we report a linguloid brachiopod species from the Upper Ordovician (Sandbian) Pingliang Formation at the Xilinggou section, southern Ordos Basin, North China Platform. Using geometric morphometrics, morphospace occupation was visualized for this species and Anomaloglossa porca, the latter of which was the most recently documented linguloid brachiopod in this section. Results indicate that the two species occupy different areas of morphospace, and the new linguloid brachiopod is assigned to Pseudolingula quadrata, which represents the first report of Pseudolingulidae from the North China Platform. Pseudolingula quadrata exhibits a clearly defined visceral area and preserves complete impressions of the musculature and mantle canal system. The absence of dorsal vascula media within the mantle canals indicates a close similarity to extant infaunal taxa. Based on geometric morphometric analysis and anatomical examination of linguloid brachiopods from the Cambrian to the present, our results not only reinforce the establishment of Pseudolingulidae at the family level, but also demonstrate significant modifications in shell shape and mantle canals that indicate their transition from an epifaunal to an infaunal lifestyle, providing critical insights into their evolutionary trajectory and ecological evolution.

Improved understanding of both the Small Skeletal Fossil (SSF) assemblages and archaeocyath reefs of the early Cambrian Period is important to best elucidate the evolution of early marine ecosystems during the Cambrian Radiation. To address this issue, we investigate the well-preserved SSF fauna associated with archaeocyaths of the early Cambrian Xiannüdong Formation (Dayingcun Section, Nanzheng area, southern Shaanxi). The Xiannüdong fossil assemblage includes sphenothallids, archaeocyaths, brachiopods, bradoriids, hyoliths, helcionelloid molluscs, trilobite sclerites, lobopods, tommotiids, chancelloriids, as well as echinoderm plates. Thin-section analysis, field observations and examination of fossil material indicate the Xiannüdong Formation assemblage consists primarily of an archaeocyath-Sphenothallus dominated ecosystem from a well-structured shallow-water mixed shelf featuring oolite shoals, archaeocyath reefs, adjacent fossiliferous allochthonous floatstone and bioclastic grain-packstone. The fossil assemblage reflects a benthic community which has not been previously described from other Cambrian reef strata of the Yangtze Platform. This unique community indicates that complex reef ecosystems were already present in the early Cambrian in this palaeogeographic region.

The major animal body plans originated during the Cambrian explosion, yet the phylum Bryozoa has remained a conspicuous exception to this pattern1. The initial discovery of Protomelission gatehousei2 provided compelling evidence for a Cambrian origin for the Bryozoa, together with other major metazoan phyla and compatible with independent molecular clock estimates3-7. Nevertheless, the scarcity of definitive soft-tissue anatomy and diagnostic skeletal microstructure has left its phylogenetic affinities ambiguous and debated8,9. Here we report exquisite fossils of P. gatehousei and a new taxon, Dayingomelission hexaclitia gen. et sp. nov., from the early Cambrian Xiannüdong Formation of China. These specimens preserve in situ phosphatized soft tissues in modular skeletons, revealing critical anatomical structures, including styles, annular muscles, membranous sacs and ring septa. This suite of traits provides definitive evidence that these taxa belong to the Bryozoa. Phylogenetic analysis incorporating these new features identifies them as crown group stenolaemates. These results confirm a Cambrian origin for the phylum and reveal an unexpected early disparity in colonial architecture, demonstrating that bryozoan diversification was an integral component of the Cambrian radiation. Moreover, the early appearance of a differentiated stenolaemate crown group indicates a still deeper origin for the bryozoan stem lineage than was first apparent.

The post-impact fauna of the Dalby Limestone of Tvären Bay has been extensively examined, with the exception of the Palaeostomate bryozoan taxa present. Here, we report three palaeostomate bryozoans found in limestone boulders recovered from glacial deposits on Ringsö Island derived from Tvären Bay, Sweden. The bryozoan fauna includes Pachydictya bifurcata, Hallopora sp., and Trematoporid sp. indet. Pachydictya bifurcata has bifoliate zoaria with two layers of zooecia oriented in opposite directions along the mesotheca. Hallopora sp. is characterized by the presence of mesozooecia, tubular autozooecia with rounded apertures, thin walls, and possessing diaphragms. The zoaria of Trematoporid sp. indet are loosely arranged and slightly ambiguous, but lack further identifying features. The report of Pachydictya bifurcata herein represents an extension of its stratigraphic range within the late Ordovician. These findings enhance our understanding of the bryozoan diversity in the region, providing the first detailed report of the presence of these taxa in this geological context.

During the early Tremadocian (Cordylodus lindstromi and Cordylodus angulatus zones), the Baltoscandian epicratonic basin displayed environmental heterogeneity. The basin included a black shale depocentre, bordered in North Estonia by coastal plains and shoal complexes featuring extensive brachiopod shell accumulations. At this juncture, obolid-dominant brachiopod communities near the shore had become extinct. Allochthonous shell beds, manifested as biogenic phosphorites, were remnants eroded from Furongian shoal bioaccumulations. Unconsolidated quartzose sand packages, displaying bidirectional cross laminae and intermittently punctuated by thin black shale intercalations and contemporaneous glendonite clusters (a pseudomorph of ikaite), were deposited in tidally influenced foreshore-to-shoreface settings. The nearshore reworking and condensation of sand phosphorites served as indicators of coastal eutrophication. This eutrophication likely led to a significant seasonal enrichment of the water column with nutrients, linked to fluctuations in dissolved oxygen. An overlooked potential contributor to this eutrophication and water pollution, coinciding with the widespread deposition of kerogenous clay and the extinction of shallow marine biota, was the rise in phosphate nutrients and an increased biomass of phytoplankton. Toxic effects were likely triggered by the extensive Furongian obolid shelly substrates, submerged during the marine transgression. The presence of substantial amounts of dissolved phosphate in the water during this period was evidenced by the deposition of concretions and crusts of chemogenic phosphorites outlining the periphery of the black shale depocentre.

Obolellids are a monophyletic group of calcareous brachiopods with a worldwide distribution that often occur near the Series 2 (Stage 4)-Miaolingian Series (Wuliuan Stage) boundary. The poorly known taxon, Obolella wirrialpensis Etheridge, 1905 originally described from the lower Cambrian Wirrealpa Limestone in the Flinders Ranges has several unique character traits including prominent "stepped" concentric lamellae and, unusually for the family, lacks any type of radial ornament. The ventral valve has a well-defined acuminate beak and single asymmetrical tooth on the left side of a raised, orthocline ventral interarea platform that aligns with a wide median notch in the dorsal valve. This unique suite of character traits reveals the taxon to be a new endemic obolellid genus, here revised as Jagoellus n. gen., part of the late Stage 4 Chalasiocranos-Kaimenella shelly fossil zone and lower Kostjubella djagoran brachiopod assemblage zone (c) 2024 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.

Cambrian Lagerstätten yield exceptionally preserved fossils that have greatly improved our understanding of the origin and evolution of animal groups. Brachiopoda, a phylum of bivalved marine invertebrates nested firmly within the lophotrochozoan protostomes, are widely recovered in such Lagerstätten. The marginal chitinous setae (or chaetae) of brachiopods are the most commonly described soft tissue and have been interpreted as performing a defensive and/or sensory role. Despite their relatively common appearance in Cambrian Lagerstätten, the origin, function, and evolution of setae in the Brachiopoda is poorly known. Here, we document exquisitely preserved setal structures from South China and Laurentia paleocontinents giving new insights into their formation, microstructure and preservation mode. New setae typically make their appearance within the follicle of a neighbouring older seta and then branches off laterally forming its own follicle. Setal microstructure is likely to be composed of many canals, highly comparable to setae of their recent counterparts. Moreover, setae recovered from these palaeo-continents present different preservation: aside from the normal preservation of iron oxides and carbonaceous ingredients, some compositions of calcium are also detected in this originally chitinous organization. Investigating the evolutionary origins of chitinous setae, a specialized type found notably in lophotrochozoans such as brachiopods and annelids, reveals its presence in early Cambrian stem groups. This character likely serves as a morphological synapomorphy in lophotrochozoan evolution. However, the dearth of morpho-ultrastructure and comparative studies in Cambrian fossils presents a challenge in fully understanding this evolutionary development.

The remarkable conservation of soft tissues within Cambrian fossils has significantly enhanced our comprehension of the origins and evolutionary trajectories of animals, in addition to the progression of ecological intricacy. Here, we report an exceptionally preserved specimen of the lingulid brachiopod Xianshanella haikouensis from the lower Cambrian Chengjiang Lagerstätte, exhibiting branched fringes along the distal ends of its marginal setae. These structures may represent either branched setae or attached macroalgae. The diameter of the branched fringes is slightly larger than that of the marginal setae, and they exhibit third- or fourth-order bifurcations, forming a complex structure comparable in length to the shell. Both the branched fringes and marginal setae are preserved as iron oxides, as revealed by SEM and Micro-XRF analyses, a characteristic preservation mode in Chengjiang fossils. The results of Micro-CT scanning suggest that these branched fringes are preserved along almost the entire distal end of marginal setae. Comparable branched fringes are reminiscent of those found in annelids, and such structural analogs between annelid and brachiopod setae support the homology of brachiopod and annelid setae, representing a lophotrochozoan synapomorphy. An alternative explanation involving attached macroalgae is proposed, given that branched setae have never been documented in either extinct or extant brachiopod taxa. If these structures represent macroalgae, this association could represent a mimicry strategy to deceive predators, although comparable macroalgal fossils remain undocumented in the Chengjiang Lagerstätte. Our research highlights the potential for brachiopod setae to serve roles in sensory function or ecological interactions, offering a new perspective on early animal adaptation and community dynamics.

Epithelial tissue may represent the earliest distinctly differentiated tissue type, but the exact timing of its emergence remains unknown. Here we present the impressions of three different types of recognizable simple epithelial cells (squamous, cuboidal, columnar) with associated nuclei, found on internal valves of specimens of the acrotretoid brachiopod Eohadrotreta zhenbaensis from the Shuijingtuo Formation (ca. 518 Ma), Three Gorges area, South China. The morphology of these cell impressions are largely similar to cell impressions found on their modern counterparts, indicating that brachiopod epithelial tissues had already achieved substantial functional differentiation by the early Cambrian. Differences in the distribution of the different epithelial cell types identified herein may potentially be responsible for regulating the overall morphology of E. zhenbaensis, with columnar impressions concentrated on the highly conical ventral valve and squamous cells more prevalent on the generally flattened dorsal valve. Detailed examination of these cell impressions not only establishes that epithelial tissues were already well-developed in Cambrian animals, but also provides valuable insights into the mineralization mechanisms that produce exoskeletal shells. square Cambrian, Brachiopods, Epithelial tissue, Nuclei, Cambrian Radiation

Living lingulide brachiopods are traditionally recognised as representatives of evolutionary conservatism, showing little change in general-morphology from their Cambrian ancestors. However, less attention has been given to their anatomical and ontogenetic modifications since their initial appearance. Among these, lingulellotretids are unique, characterized by their typical elongate pedicle foramen and large pseudointerarea. This study describes exquisitely preserved soft-tissue and phosphatic shells of Lingulellotreta from Cambrian Series 2 deposits in China and Kazakhstan. Biomineralized novelties in Lingulellotreta, including elongate pseudointerarea forming a pouch-like visceral cavity and columnar shell architecture, probably were evolutionarily modified from the unmineralized tubular ancestor Yuganotheca during the Cambrian Explosion. Lingulellotretids, however, faced extinction in the Early Ordovician, exemplifying a short-lived evolutionary experiment with a tubular body form in early brachiopods. Since the early Cambrian, lingulide brachiopods have exhibited a long-term evolutionary trend marked by the reduction of pseudointerarea, reflecting a convergence toward a more efficient body plan that ultimately became dominant in later lineages. The intensification of skeletal defences and the increasing demands of filter feeding within benthic communities likely drove these evolutionary modifications and ecological adjustments, culminating in the development of the distinctive, persistent tongue-shaped body of linguloid brachiopods during the Great Ordovician Biodiversification Event. Tubular lingulellotretid brachiopods, exemplifying a short-lived evolutionary experiment during the Cambrian explosion, gave way to the more efficient tongue-shaped body plan of lingulides by the evolutionary reduction of pseudointerarea.

Three exceptionally preserved, silicified and articulated complete shells with pedicles of kutorginate brachiopods are described from the Cambrian Burj Formation (latest Stage 4) of Jordan. One specimen can be assigned to Trematosia radifer (Cooper) and the others represent a new unnamed species of Kutorgina. The silicified pedicles differ significantly from those of living crown group rhynchonelliforms. In Kutorgina it is strongly annulated, whilst that of Trematosia is smooth; both taper distally and are likely much more flexible as compared with pedicles of living brachiopods. The silicified pedicles are more similar to the exceptionally preserved pedicles from other Cambrian rhynchonelliform brachiopods-like Longtancunella and Alisina. However, pedicles of the latter emerge from the ventral apical foramen rather than from the opening between the valves as in the new specimens from Jordan. Although generally similar, these two types of pedicles are unlikely to represent homologous structures. Both kutorginates possesses both an apical foramen (potentially representing a non-functional vestigial attachment) and a posterior adult pedicle. The similarities between the pedicles may be attributed to a similar type of accretionary growth from two different types of epithelia. The kutorginate-like pedicle most likely appeared early within the kutorginates and rhynchonellates. square Brachiopoda, Kutorginida, Cambrian, Lagerst & auml;tte, Jordan, pedicle.

Biologically-controlled mineralization producing organic-inorganic composites (hard skeletons) by metazoan biomineralizers has been an evolutionary innovation since the earliest Cambrian. Among them, linguliform brachiopods are one of the key invertebrates that secrete calcium phosphate minerals to build their shells. One of the most distinct shell structures is the organo-phosphatic cylindrical column exclusive to phosphatic-shelled brachiopods, including both crown and stem groups. However, the complexity, diversity and biomineralization processes of these microscopic columns are far from clear in brachiopod ancestors. Here, exquisitely well-preserved columnar shell ultrastructures are reported for the first time in the earliest eoobolids Latusobolus xiaoyangbaensis gen. et sp. nov. and Eoobolus acutulus sp. nov from the Cambrian Series 2 Shuijingtuo Formation of South China. The hierarchical shell architectures, epithelial cell moulds, and the shape and size of cylindrical columns are scrutinised in these new species. Their calcium phosphate-based biomineralized shells are mainly composed of stacked sandwich columnar units. The secretion and construction of the stacked sandwich model of columnar architecture, which played a significant role in the evolution of linguliforms, is highly biologically controlled and organic-matrix mediated. Furthermore, a continuous transformation of anatomic features resulting from the growth of diverse columnar shells is revealed between Eoobolidae, Lingulellotretidae and Acrotretida, shedding new light on the evolutionary growth and adaptive innovation of biomineralized columnar architecture among early phosphatic-shelled brachiopods during the Cambrian explosion.

Antarctica and Australia were sutured together at the equator during the major pulse of animal biodiversification associated with the Cambrian radiation. However, the lack of detailed systematic chemostratigraphic and biostratigraphic sampling of lower Cambrian sedimentary successions from Antarctica has significantly impeded precise age determination and correlation with Cambrian strata on other palaeocontinents. This study is the first to present integrated, simultaneously sampled biostratigraphic and chemostratigraphic (d13C isotopes) data from the same measured stratigraphic sections through the lower Cambrian Byrd Group in the Transantarctic Mountains. Shelly fossil assemblages (brachiopods, tommotiids, molluscs, bradoriids, trilobites) from the Holyoake Range and Churchill Mountains facilitate direct correlation with the Dailyatia odyssei Zone of South Australia (Cambrian Stages 3-4), and trilobites provide strong correlation between the Starshot Formation and the Cymbric Vale Formation in western New South Wales. A new ID-TIMS radiometric date of 514.96 +/- 0.16 Ma from a tuff in the lower Cymbric Vale Formation is similar to dates from tuff beds in the Third Plain Creek Member of the Mernmerna Formation in the Flinders Ranges, providing an important absolute-age tie point between these lower Cambrian successions. Chemostratigraphic data from the upper Shackleton Limestone in the Holyoake Range capture a negative d13C excursion that can be correlated to negative values within the multipeaked MICE (cycles V-VIII in Siberia). Integrated faunal and chemostratigraphic data indicate a Cambrian Stages 3-4 age, giving robust chronostratigraphic context for the upper Shackleton Limestone-Holyoake Formation-Starshot Formation succession for the first time, permitting reconstruction of the depositional history of the lower Cambrian of Antarctica and global correlation of Byrd Group strata. (c) 2024 International Association for Gondwana Research. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The evolution of brachiopod symbiosis is closely tied to the evolution of brachiopod faunas and their partner groups during the early Palaeozoic. Brachiopod groups with a larger number of taxa had more symbiotic associations, and there was no specific group that was more prone to symbiosis during this time interval. The first symbiotic associations appeared soon after the emergence of certain brachiopod groups, with Cambrian brachiopods partnering with typical representatives of the Cambrian fauna. Bryozoans and tentaculitoid tubeworms, which became important partners during the Ordovician and Silurian, first diversified in the Ordovician. The gradual decrease in the number of brachiopod partner groups from the Cambrian to the Silurian was likely due to specialisation. However, the number of symbiotic associations did not increase faster than the number of brachiopod taxa. The GOBE-induced diversification of brachiopod taxa did not lead to an escalation in symbiotic relationships. Symbiotic associations involving brachiopods continued after the end-Ordovician mass extinction. Although early Palaeozoic brachiopods were vulnerable to kleptoparasites, the harm caused by these parasites was not enough to drive their associated brachiopods to extinction.

Brachiopods first appeared in the early Cambrian and persist till present. They are one of the main lineages of marine invertebrates that diversified throughout the Paleozoic and reached their maximum diversity of highrank taxonomy during the Ordovician. During this time interval, brachiopods were mainly dominated by the articulated Orthida and Strophomenida, which represent major components of the Paleozoic Evolutionary Fauna; however, the inarticulated lingulid brachiopods (Order Lingulida) were comparatively less abundant and received less attention during this time period. Here, we report a new record of the lingulid brachiopod Anomaloglossa porca from the Upper Ordovician (Sandbian) Pingliang Formation of the Xilinggou Section, Shaanxi Province, North China. Collected specimens are preserved as calcium phosphatic shells with highly mineralization which preserve detailed morphology and shell ornamentation of both ventral and dorsal valves. The new occurrence of A. porca extends its paleogeographic distribution from Gondwana and Tarim to North China Platform. Moreover, comprehensive geometric morphometric analysis of A. porca is performed and the results indicate that both the shell shape and pseudointerarea are very close to the recent infaunal lingulids. If interpreted correctly, the fossils represent the first example of infaunal lifestyles achieved by Ordovician lingulids from North China, exhibiting the ecological complexities of the Late Ordovician benthos composed of epibenthos and infaunas as well.

Diandongia pista Rong is the thickest-shelled and strongly mineralized of all the brachiopods that have been recorded from the Chengjiang Fauna. It is also one of the most common species in the biota. Previous accounts have concentrated largely on the exceptionally preserved soft-bodied anatomy of this species. Here its detailed internal and external shell morphologies are described for the first time, based on BSEM and SEM observations. Its general shell morphology, pseudointerareas, and pustulose ornamentation are most similar to those of the Botsfordiidae, where many species have a Diandongia-like rhombic pattern of pustules in the juvenile apical region only. On the other hand, other aspects of the muscle pattern and the partly smooth adult ornamentation of D. pista is more suggestive of species within the Neobolidae, like Edreja. The mantle canal system in sub-adults of D. pista is comparable to that of the Eoobolidae and Obolidae, whereas the adult vascular system branches peripherally in dichotomy. D. pista may be the earliest representatives possessing some plesiomorphic characters of the Botsfordiidae.

Abstract Biologically controlled mineral crystals producing organic-inorganic composites (hard skeletons) by metazoan biomineralizers has been an evolutionary innovation for more than half billion years on Earth. Among them, linguliform brachiopods are the only invertebrates that secrete phosphate to build their skeletons. One of the most distinct shell structures is the organic-phosphatic columns applied exclusively by phosphatic-shelled brachiopods. However, the complexity, diversity and biomineralization process of these microscopic columns are far from clear in brachiopod ancestors. Here, exquisitely well preserved columnar structures are discovered for the first time in the earliest eoobolids. The hierarchical shell architectures, epithelial cell moulds, and the shape and size of cylindrical columns are scrutinised in Latusobolus xiaoyangbaensis gen. et sp. nov. and Eoobolus acutulus sp. nov from the Cambrian Series 2 Shuijingtuo Formation of South China. The secretion and construction of the stacked sandwich model of columnar shell, which played a significant role in the evolution of linguliforms, is highly biologically controlled and organic- matrix mediated. Furthermore, a continuous transformation of anatomic features resulting from the growth of columns is revealed between Eoobolidae, Lingulellotretidae and Acrotretida, shedding new light on the evolutionary growth and adaptive innovation of stacked sandwich columns among early phosphatic-shelled brachiopods during the Cambrian explosion.