| 1. |
- Li, Luoyang, et al.
(författare)
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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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Ingår i: Biology. - : MDPI. - 2079-7737. ; 12:1, s. 113-113
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Li, Luoyang, et al.
(författare)
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HOMOLOGOUS SHELL MICROSTRUCTURES INCAMBRIAN HYOLITHS AND MOLLUSCS
- 2019
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 62:4, s. 515-532
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Li, Luoyang, et al.
(författare)
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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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Ingår i: Papers in Palaeontology. - : John Wiley & Sons. - 2056-2799 .- 2056-2802. ; 7:1, s. 521-564
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Li, Luoyang, et al.
(författare)
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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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Ingår i: Journal of Systematic Palaeontology. - : Informa UK Limited. - 1477-2019 .- 1478-0941. ; 17, s. 1699-1709
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Tidskriftsartikel (refereegranskat)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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| 5. |
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| 6. |
- Yun, Hao, et al.
(författare)
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Biomineralization of the Cambrian chancelloriids
- 2021
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Ingår i: Geology. - : Geological Society of America. - 0091-7613 .- 1943-2682. ; 49, s. 623-
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Li, Luoyang, et al.
(författare)
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New insight into the soft anatomy and shell microstructures of early Cambrian orthothecids (Hyolitha)
- 2020
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 287
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Tidskriftsartikel (refereegranskat)abstract
- Hyoliths (hyolithids and orthothecids) were one of the most successful early biomineralizing lophotrochozoans, and were a key component of the Cambrian evolutionary fauna. However, the morphology, skeletogenesis and anatomy of earliest members of this enigmatic clade, as well as its relationship with other lophotrochozoan phyla remain highly contentious. Here we present a new orthothecid, Longxiantheca mira gen. et sp. nov. preserved as part of the secondarily phosphatized Small Shelly Fossil assemblage from the lower Cambrian Xinji Formation of North China. Longxiantheca mira retains some ancestral traits of the clade with an undifferentiated disc-shaped operculum and a simple conical conch with a two-layered microstructure of aragonitic fibrous bundles. The operculum interior exhibits impressions of soft tissues, including muscle attachment scars, mantle epithelial cells and a central kidney-shaped platform in association with its feeding organ. Our study reveals that the muscular system and tentaculate feeding apparatus in orthothecids appear to be similar to that in hyolithids, suggesting a consistent anatomical configuration among the total group of hyoliths. The new finding of shell secreting cells demonstrates a mantle regulating mode of growth for the operculum. Taking all these data into considerations, especially on the basis of shell microstructures, we argue that hyoliths were an extinct sister group of molluscs.
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| 8. |
- Li, Luoyang, et al.
(författare)
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Qingjianglepas from the Qingjiang biota, an evolutionary dead-end of Cambrian helcionelloid mollusks?
- 2021
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 575, s. 110480-110480
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Tidskriftsartikel (refereegranskat)abstract
- A minute limpet-shaped shell, Qingjianglepas elegans n. gen. n. sp., is reported from the 518 million-year-old Qingjiang biota in Hubei, China. The new shell exhibits a typical limpet morphology with a shell sculpture of strongly developed radial ribs, an anterior shell fold, and distinctive shell shape shift. Feature combinations such as in Qingjianglepas are unique among Cambrian mollusk assemblages, but strikingly resemble that of some modern fissurellids (keyhole and slit limpets; Vetigastropoda). The biological affinity of Qingjianglepas is discussed, but temporarily remains uncertain. Regardless, the heavily sculptured and limpet-shaped Qingjianglepas represents a previously unrecognized shell form, and hence significantly extends the morphological diversity of Cambrian mollusks. The abrupt ontogenetic change in shell morphology suggests that Qingjianglepas might change microhabitat throughout the growth of the animal. This study reveals that the phenomenon of limpetization occurred within early Cambrian total-group conchiferans. Furthermore, Qingjianglepas might represent an evolutionary dead-end in course of helcionelloid mollusk evolution, which marks the end of the Cambrian explosion of animals at the beginning of Cambrian Series 2.
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| 9. |
- Yun, Hao, et al.
(författare)
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Pyritized preservation of chancelloriids from the Cambrian Stage 3 ofSouth China and implications for biomineralization
- 2021
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Ingår i: Geobios. - Amsterdam : Elsevier BV. - 0016-6995 .- 1777-5728. ; 69, s. 77-86
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Tidskriftsartikel (refereegranskat)abstract
- The enigmatic Cambrian animal chancelloriids were discovered in a wide range of taphonomic settings; however, preservation of biomineralized sclerite microstructure was solely known from secondarily phosphatized skeletal remains. Here, we investigate a uniquely pyritized chancelloriid from the lowerCambrian Guojiaba Formation in southern Shaanxi Province, China, using a combination of advanced analytic techniques. Results of the energy dispersive spectroscopy (EDS), X-Ray Fluorescence (XRF), and Raman spectrum show that the sclerites and scleritomes are preserved as pyritized internal moulds witha calcitic outer layer. The outer layer enveloping the internal moulds likely represents the recrystallized counterpart of the original biomineralized sclerite wall. Distinctive fibrous microstructures are discovered in the sclerites, which echo the features seen in the phosphatized fossils of chancelloriids. The typical microstructure, along with the recrystallized calcite, corroborate the interpretation that chancelloriid sclerites were originally constructed by fibrous aragonite. The stability of the microstructure and mineral composition in both carbonate and siliciclastic backgrounds indicate that chancelloriids were adapted to exploit aragonitic fibres to build their skeletons regardless of the change of their living environments.
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