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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 post-impact fauna of the Dalby Limestone of TvÀren 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 TvÀren 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.

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.

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.

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 (δ¹³C 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 δ¹³C excursion that can be correlated to negative values within the multi-peaked 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.

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 high-rank 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.

A steinkern of an endoceratid nautiloid siphuncle contains a Trypanites sozialis boring with a lingulate brachiopod Rowellella sp. shell inside. The steinkern of this endoceratid formed during early lithification of the sediment on the seafloor. The lithified steinkern of this siphuncle was either initially partially exposed to the seawater or was exhumed and stayed exposed on the seafloor, where it was colonized by boring organisms. This bioerosion resulted in numerous Trypanites borings in the siphuncle. After the death or exit of the Trypanites trace maker, a vacant boring was colonized by a small lingulate nestler Rowellella sp. This lingulate was likely preadapted to life in hard substrate borings when it first found its way into borings in living substrates in the Late Ordovician. The increased availability of hard substrate borings, combined with the increased predation pressure due to the GOBE, enhanced the colonization of hard substrate borings by lingulate brachiopods.

Summary Morphology usually serves as an effective proxy for functional ecology,1,2,3,4,5 and evaluating morphological, anatomical, and ecological changes permits a deeper understanding of the nature of diversification and macroevolution.5,6,7,8,9,10,11,12 Lingulid (order Lingulida) brachiopods are both diverse and abundant during the early Palaeozoic but decrease in diversity over time, with only a few genera of linguloids and discinoids present in modern marine ecosystems, resulting in them frequently being referred to as “living fossils.”13,14,15 The dynamics that drove this decline remain uncertain, and it has not been determined if there is an associated decline in morphological and ecological diversity. Here, we apply geometric morphometrics to reconstruct global morphospace occupation for lingulid brachiopods through the Phanerozoic, with results showing that maximum morphospace occupation was reached by the Early Ordovician. At this time of peak diversity, linguloids with a sub-rectangular shell shape already possessed several evolutionary features, such as the rearrangement of mantle canals and reduction of the pseudointerarea, common to all modern infaunal forms. The end Ordovician mass extinction has a differential effect on linguloids, disproportionally wiping out those forms with a rounded shell shape, while forms with sub-rectangular shells survived both the end Ordovician and the Permian-Triassic mass extinctions, leaving a fauna predominantly composed of infaunal forms. For discinoids, both morphospace occupation and epibenthic life strategies remain consistent through the Phanerozoic. Morphospace occupation over time, when considered using anatomical and ecological analyses, suggests that the limited morphological and ecological diversity of modern lingulid brachiopods reflects evolutionary contingency rather than deterministic processes.

A small skeletal fossil assemblage is described for the first time from the bioclastic limestone interbeds of the siltstone-dominated Guojiaba Formation, southern Shaanxi, China. The carbonate-hosted fossils include brachiopods (Eohadrotreta zhujiahensis, Eohadrotreta zhenbaensis, Spinobolus sp., Kuangshanotreta malungensis, Kyrshabaktella sp., Lingulellotreta yuanshanensis, Eoobolus incipiens, and Eoobolus sp.), sphenothallids (Sphenothallus sp.), archaeocyaths (Robustocyathus sp. and Yukonocyathus sp.), bradoriids (Kunmingella douvillei), chancelloriids sclerites (Onychia sp., Allonnia sp., Diminia sp., Archiasterella pentactina, and Chancelloria cf. eros), echinoderm plates, fragments of trilobites (Eoredlichia sp.), and hyolithelminths. The discovery of archaeocyaths in the Guojiaba Formation significantly extends their stratigraphic range in South China from the early Tsanglangpuian at least to the late Chiungchussuan. Thus, the Guojiaba Formation now represents the lowest known stratigraphic horizon where archaeocyath fossils have been found in the southern Shaanxi area. The overall assemblage is most comparable, in terms of composition, to Small skeletal fossil (SSF) assemblages from the early Cambrian Chengjiang fauna recovered from the Yu’anshan Formation in eastern Yunnan Province. The existing position that the Guojiaba Formation is correlated with Stage 3 in Cambrian Series 2 is strongly upheld based on the fossil assemblage recovered in this study.

Simple Summary

Small skeletal fossils are reported for the first time from the early Cambrian Guojiaba Formation, southern Shaanxi, China. All specimens were recovered from bioclastic limestone interbeds and encompass a wide variety of skeletal clades, including brachiopods, sphenothallids, archaeocyaths, bradoriids, sponge spicules, echinoderm plates, and trilobite spines. The archaeocyaths described herein are considerably older than those described from the Xiannvdong Formation, which was previously assumed to contain the lowest archaeocyath-bearing horizons in South China. The brachiopod Lingulellotreta yuanshanensis is recorded for the first time from the Fucheng area, with previous records confined mainly to the Chengjiang Fauna-bearing Yu’anshan Formation in the lower Cambrian, the eastern Yunnan Province. Micro-morphological and elemental analyses of the small skeletal fossil assemblages were carried out using SEM, BSEM, and Micro X–ray fluorescence. The skeletal fauna in the Guojiaba Formation resembles the assemblages recovered from the upper Yu’anshan Formation (Chengjiang Fauna) in eastern Yunnan Province. Based on the recovered assemblage, the biostratigraphic age of the Guojiaba Formation correlates with the Chiungchussuan Stage (Stage 3 of Cambrian Series 2).