| 1. |
- Pan, Bing, et al.
(author)
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Early Cambrian organophosphatic brachiopods from the Xinji Formation, at Shuiyu section, Shanxi Province, North China
- 2020
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In: Palaeoworld. - : Elsevier BV. - 1871-174X .- 1875-5887. ; 29:3, s. 512-533
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Journal article (peer-reviewed)abstract
- Abundant and diverse small shelly fossils have been reported from Cambrian Series 2 in North China, but the co-occurring brachiopods are still poorly known. Herein, we describe seven genera, five species and two undetermined species of organophosphatic brachiopods including one new genus and new species from the lower Cambrian Xinji Formation at Shuiyu section, located on the southern margin of North China Platform. The brachiopod assemblage comprises one mickwitziid (stem group brachiopoda), Paramickwitzia boreussinaensis n. gen. n. sp., a paterinide, Askepasma toddense Laurie, 1986, an acrotretoid, Eohadrotreta cf. zhenbaensis Li and Holmer, 2004, a botsfordiid, Schizopholis yorkensis (Holmer and Ushatinskaya in Gravestock et al., 2001) and three linguloids, Spinobolus sp., Eodicellomus cf. elkaniiformis Holmer and Ushatinskaya in Gravestock et al., 2001 and Eoobolus sp. This brachiopod assemblage suggests a late Age 3 to early Age 4 for the Xinji Formation and reveals a remarkably strong connection with coeval faunas from East Gondwana, particularly the Hawker Group in South Australia. The high degree of similarity (even at species level) further supports a close palaeogeographic position between the North China Platform and Australian East Gondwana during the early Cambrian as indicated by small shelly fossil data.
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| 2. |
- Goñi, Iban, et al.
(author)
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New Palaeoscolecid plates from the Cambrian Stage 3 of northern Mongolia
- 2023
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In: Acta Palaeontologica Polonica. - : Polska Akademia Nauk Instytut Paleobiologii (Institute of Paleobiology, Polish Academy of Sciences). - 0567-7920 .- 1732-2421. ; 68
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Journal article (peer-reviewed)abstract
- New material of disarticulated paleoscolecid remains have been found in “Small Shelly/Skeletal Fossils” assemblages from Cambrian Stage 3 extracted from a section in the Khubsugul Lake region of northern Mongolia. The current material is composed of isolated phosphatic plates, rendering the whole-body reconstruction and comparisons difficult. However, the morphology of the plates is unique enough to warrant description of a new genus and species Floraconformis egiinensis. The new taxon is characterised by a stellate depression network spreading from the middle that separates numerous elevations. Floraconformis egiinensis gen. et sp. nov. represents one of the oldest records of isolated palaeoscolecid plates.
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| 3. |
- Li, Luoyang, et al.
(author)
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Calcitic shells in the aragonite sea of the earliest Cambrian
- 2023
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In: Geology. - USA : Geological Society of America. - 0091-7613 .- 1943-2682.
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Journal article (peer-reviewed)abstract
- The initial acquisition of calcium carbonate polymorphs (aragonite and calcite) at the onset of skeletal biomineralization by disparate metazoans across the Ediacaran-Cambrian transition is thought to be directly influenced by Earth’s seawater chemistry. It has been presumed that animal clades that first acquired mineralized skeletons during the so-called “aragonite sea” of the latest Ediacaran and earliest Cambrian (Terreneuvian) possessed aragonite or high-Mg calcite skeletons, while clades that arose in the subsequent “calcite sea” of Cambrian Series 2 acquired low-Mg calcite skeletons. Here, contrary to previous expectations, we document shells of one of the earliest helcionelloid molluscs from the basal Cambrian of southwestern Mongolia that are composed entirely of low-Mg calcite and formed during the Terreneuvian aragonite sea. The extraordinarily well-preserved Postacanthellashells have a simple prismatic microstructure identical to that of their modern low-Mg calcite molluscan relatives. High-resolution scanning electron microscope observations show that calcitic crystallites were originally encased within an intra- and interprismatic organic matrix scaffold preserved by aggregates of apatite during early diagenesis. This indicates that not all molluscan taxa during the early Cambrian produced aragonitic shells, weakening the direct link between carbonate skeletal mineralogy and ambient seawater chemistry during the early evolution of the phylum. Rather, our study suggests that skeletal mineralogy in Postacanthella was biologically controlled, possibly exerted by the associated prismatic organic matrix. The presence of calcite or aragonite mineralogy in different early Cambrian molluscan taxa indicates that the construction of calcium carbonate polymorphs at the time when skeletons first emerged may have been species dependent
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| 4. |
- Li, Luoyang, et al.
(author)
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Fibrous or Prismatic? A Comparison of the Lamello-Fibrillar Nacre in Early Cambrian and Modern Lophotrochozoans
- 2023
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In: Biology. - : MDPI. - 2079-7737. ; 12:1, s. 113-113
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Journal article (peer-reviewed)abstract
- The Precambrian–Cambrian interval saw the first appearance of disparate modern metazoan phyla equipped with a wide array of mineralized exo- and endo-skeletons. However, the current knowledge of this remarkable metazoan skeletonization bio-event and its environmental interactions is limited because uncertainties have persisted in determining the mineralogy, microstructure, and hierarchical complexity of these earliest animal skeletons. This study characterizes in detail a previously poorly understood fibrous microstructure—the lamello-fibrillar (LF) nacre—in early Cambrian mollusk and hyolith shells and compares it with shell microstructures in modern counterparts (coleoid cuttlebones and serpulid tubes). This comparative study highlights key differences in the LF nacre amongst different lophotrochozoan groups in terms of mineralogical compositions and architectural organization of crystals. The results demonstrate that the LF nacre is a microstructural motif confined to the Mollusca. This study demonstrates that similar fibrous microstructure in Cambrian mollusks and hyoliths actually represent a primitive type of prismatic microstructure constituted of calcitic prisms. Revision of these fibrous microstructures in Cambrian fossils demonstrates that calcitic shells are prevalent in the so-called aragonite sea of the earliest Cambrian. This has important implications for understanding the relationship between seawater chemistry and skeletal mineralogy at the time when skeletons were first acquired by early lophotrochozoan biomineralizers.
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| 5. |
- Li, Luoyang, et al.
(author)
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HOMOLOGOUS SHELL MICROSTRUCTURES INCAMBRIAN HYOLITHS AND MOLLUSCS
- 2019
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In: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 62:4, s. 515-532
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Journal article (peer-reviewed)abstract
- Hyoliths were among the earliest biomineralizingmetazoans in Palaeozoic marine environments. They havebeen known for two centuries and widely assigned tolophotrochozoans. However, their origin and relationshipswith modern lophotrochozoan clades have been a longstand-ing palaeontological controversy. Here, we provide broadmicrostructural data from hyolith conchs and opercula fromthe lower Cambrian Xinji Formation of North China, includ-ing two hyolithid genera and four orthothecid genera as wellas unidentified opercula. Results show that most hyolithconchs contain a distinct aragonitic lamellar layer that is com-posed of foliated aragonite, except in the orthothecid Newtaxon 1 that has a crossed foliated lamellar microstructure.Opercula are mostly composed of foliated aragonite andoccasionally foliated calcite. These blade or lath-likemicrostructural fabrics coincide well with biomineralizationof Cambrian molluscs rather than lophophorates, as exempli-fied by the Cambrian members of the tommotiid-brachiopodlinage. Accordingly, we propose that hyoliths and molluscsmight have inherited their biomineralized skeletons from anon-mineralized or weakly mineralized common ancestorrather than as a result of convergence. Consequently, fromthe view of biomineralization, the homologous shellmicrostructures in Cambrian hyoliths and molluscs stronglystrengthen the phylogenetic links between the two groups.
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| 6. |
- Li, Luoyang, et al.
(author)
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Revisiting the molluscan fauna from the Cambrian (Series 2, stages 3–4) Xinji Formation of North China
- 2021
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In: Papers in Palaeontology. - : John Wiley & Sons. - 2056-2799 .- 2056-2802. ; 7:1, s. 521-564
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Journal article (peer-reviewed)abstract
- A diverse group of molluscs from the Cambrian Series 2, Stages 3–4 Xinji Formation of the North China Block (NCB) is described, based on more than 4500 specimens from three well-studied sections in Shaanxi and Henan provinces, along the southern and southwestern margin of the NCB. Twenty molluscan species are identified, including one bivalve, three stem group gastropods, and 16 additional helcionelloids. Among these, six helcionelloid species are reported from the NCB for the first time, and one new species, Parailsanella luonanensis sp. nov. is proposed. This diverse molluscan fauna shares a large number of species with contemporaneous faunas of South Australia (15), Antarctica (7), Laurentia (6), Siberia (3) and South China (1). Faunal similarities are even greater on a generic level. The striking similarities of the molluscan faunas of North China, South Australia and Antarctica strongly support the hypothesis that the NCB was situated close to Eastern Gondwana, most likely close to South Australia in the Cambrian Epoch 2. In addition, well-preserved shell attachment muscle scars were observed in the helcionelloid Figurina figurina, with two pairs of symmetrical, continuous, band-like muscle scars, which are obviously different from the musculature of both gastropods and monoplacophorans. Because of this unique musculature, these characteristic Cambrian cap-like molluscs are assigned to the Helcionelloida rather than to the Gastropoda or Monoplacophora. A diverse group of molluscs from the Cambrian Series 2, Stages 3–4 Xinji Formation of the North China Block (NCB) is described, based on more than 4500 specimens from three well-studied sections in Shaanxi and Henan provinces, along the southern and southwestern margin of the NCB. Twenty molluscan species are identified, including one bivalve, three stem group gastropods, and 16 additional helcionelloids. Among these, six helcionelloid species are reported from the NCB for the first time, and one new species, Parailsanella luonanensis sp. nov. is proposed. This diverse molluscan fauna shares a large number of species with contemporaneous faunas of South Australia (15), Antarctica (7), Laurentia (6), Siberia (3) and South China (1). Faunal similarities are even greater on a generic level. The striking similarities of the molluscan faunas of North China, South Australia and Antarctica strongly support the hypothesis that the NCB was situated close to Eastern Gondwana, most likely close to South Australia in the Cambrian Epoch 2. In addition, well-preserved shell attachment muscle scars were observed in the helcionelloid Figurina figurina, with two pairs of symmetrical, continuous, band-like muscle scars, which are obviously different from the musculature of both gastropods and monoplacophorans. Because of this unique musculature, these characteristic Cambrian cap-like molluscs are assigned to the Helcionelloida rather than to the Gastropoda or Monoplacophora.
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| 7. |
- Li, Luoyang, et al.
(author)
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Shell microstructures of the helcionelloid mollusc Anabarella australis from the lower Cambrian (Series 2) Xinji Formation of North China
- 2019
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In: Journal of Systematic Palaeontology. - : Informa UK Limited. - 1477-2019 .- 1478-0941. ; 17, s. 1699-1709
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Journal article (peer-reviewed)abstract
- Although various types of shell microstructures are documented from Cambrian molluscs, the precise organization and mineralogical composition of Terreneuvian molluscs are relatively unknown. Anabarella was one of the first helcionellid molluscs to appear in the Terreneuvian, with the genus surviving until the third epoch of the Cambrian. Here, shell microstructures of Anabarella australis have been studied based on new collections from the lower Cambrian (Series 2) Xinji Formation of the North China Block. Results show that A. australis has a laminar inner shell layer that consists of crossed foliated lamellar microstructure (CFL). Nacreous, crossed-lamellar and foliated aragonite microstructures previously documented in the older (Terreneuvian) species A. plana are here revised as preservational artefacts of the CFL layers. This complex skeletal organization of Anabarella suggests that mechanisms of molluscan biomineralization evolved very rapidly. Morphologically, specimens from the Chaijiawa section show a pattern of distinct ‘pseudo-dimorphism’ as external coatings are identical to Anabarella, while associated internal moulds are similar to the helcionelloid genus Planutenia. In contrast, internal moulds from the Shangzhangwan section show considerable morphological variation owing to preservational bias and show greater similarities to specimens from South Australia, Northeast Greenland and Germany. These observations demonstrate that the extensive morphological variation seen in the internal moulds of the cosmopolitan genus Anabarella are primarily preservational artefacts and are unlikely to represent the real intra- and interspecific variability of the animal. In these cases, Planutenia is here confirmed to be a subjective synonym of Anabarella.
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| 8. |
- Skovsted, Christian, 1974-, et al.
(author)
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On the origin of hyolith helens
- 2020
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In: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 555
-
Journal article (peer-reviewed)abstract
- Helens, the curved lateral spines inserted between the conch and operculum of some hyoliths, are a unique morphological adaptation characterizing the order Hyolithida. These structures are paired, movable and had a mechanical function, probably related to orienting the hyolith conch and lifting its aperture above the sea floor. We show that helens are intimately associated with the hyolith opercula and are structurally comparable to the rod like units that constitute the clavicles, internal wall-like structures of the hyolithid operculum that probably evolved to secure the operculum from lateral displacement in the conch aperture. In some early Cambrian hyolith taxa that lack helens, such as Paramicrocornus, new clavicle rods are added in the gap separating the clavicles from the cardinal processes, the same position where helens are inserted in later hyolithids. We also show that the size of incipient helens at the earliest ontogenetic stage matches the size of the clavicles in associated opercula. We propose that helens are modified clavicle rods that were detached from the operculum and developed into lateral spines through allometric growth during early ontogeny. Further, we suggest a four-step model for the evolution of hyolithid hyoliths from orthothecid ancestors: 1, Externally fitting operculum; 2, Stabilizing, radially arranged structures on the inside of the operculum; 3, Ligula and folded operculum; 4, Detachment of clavicle rods and origin of helens.
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| 9. |
- Topper, Timothy, et al.
(author)
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Locating the BACE of the Cambrian: Bayan Gol in southwestern Mongolia and global correlation of the Ediacaran–Cambrian boundary
- 2022
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In: Earth-Science Reviews. - Amsterdam : Elsevier. - 0012-8252 .- 1872-6828. ; 229, s. 104017-104017
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Journal article (peer-reviewed)abstract
- The diversification of animals during the Cambrian Period is one of the most significant evolutionary events inEarth’s history. However, the sequence of events leading to the origin of ‘modern’ ecosystems and the exacttemporal relationship between Ediacaran and Cambrian faunas are uncertain, as identification of the Ediacaran–Cambrian boundary and global correlation through this interval remains problematic. Here we review thecontroversies surrounding global correlation of the base of the Cambrian and present new high-resolutionbiostratigraphic, lithostratigraphic and δ13C chemostratigraphic data for terminal Ediacaran to basal Cambrianstrata in the Zavkhan Basin of Mongolia. This predominantly carbonate sequence, through the Zuun-Arts andBayangol formations in southwestern Mongolia, captures a distinct, negative δ13C excursion close to the top ofthe Zuun-Arts Formation recognized as the BAsal Cambrian carbon isotope Excursion (BACE). In this location,the nadir of the BACE closely coincides with first occurrence of the characteristic early Cambrian protoconodontProtohertzina anabarica. Despite recent suggestions that there is an evolutionary continuum of biomineralizinganimals across the Ediacaran–Cambrian transition, we suggest that this continuum is restricted to tubular forms,and that skeletal taxa such as Protohertzina depict ‘true’ Cambrian representatives that are restricted entirely tothe Cambrian. Employing the first appearance of the trace fossil Treptichnus pedum to define the base of theCambrian suffers significant drawbacks, particularly in carbonate settings where it is not commonly preserved.As T. pedum is the only proxy available to correlate the Cambrian Global boundary Stratotype Section and Point(GSSP) defined at Fortune Head, Newfoundland, we suggest that the GSSP be redefined elsewhere, in a newstratigraphic section that contains secondary markers that permit global correlation. We propose the nadir of theBACE as the favored candidate to define the base of the Cambrian. However, it is essential that the BACE becomplemented with secondary markers. In many global sections the nadir of the BACE and the first occurrence ofthe genus Protohertzina are closely juxtaposed, as are the BACE and T. pedum. Hence these taxa provide essentialbiostratigraphic control on the BACE and increase potential for effective global correlation. We also recommendthat an Auxiliary boundary Stratotype Section and Point (ASSP) be simultaneously established in order toincorporate additional markers that will aid global correlation of the Ediacaran–Cambrian boundary. The BAY4/5 section through the upper Zuun-Arts and Bayangol formations yields key shelly fossils and δ13C values and istherefore an ideal candidate for consideration as the GSSP for the Ediacaran–Cambrian boundary.
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| 10. |
- Yun, Hao, et al.
(author)
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Biomineralization of the Cambrian chancelloriids
- 2021
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In: Geology. - : Geological Society of America. - 0091-7613 .- 1943-2682. ; 49, s. 623-
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Journal article (peer-reviewed)abstract
- As extinct animals that flourished during the Cambrian explosion, chancelloriids have a unique body plan lacking guts but with a flexible integument and a suite of star-shaped, hollow sclerites. Due to this body plan, along with the paucity of knowledge on sclerite biomineralization, the phylogenetic position of chancelloriids within the Metazoa is still controversial. Integration of analyses of diverse fossils from Cambrian stage 2 to the Wuliuan Stage of China and Australia indicates that chancelloriid sclerites possess an encasement-like organic layer and a fibrous aragonitic layer. The organic layer is inferred to be a specialized trait derived from the epidermal integument of the animal body. The sclerites were likely biomineralized by using the outer organic layer as a template to absorb cations and precipitate crystal nuclei, reflecting a strategy adopted by a range of eumetazoans with a developed epidermis. Therefore, the hypothesis that chancelloriids represent an epitheliozoan-grade animal and an early explorer of template-based biomineralization is supported.
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