Bryozoans from the early Cambrian Chengjiang Biota

Abstract Bryozoa are colonial, aquatic, generally sessile coelomate metazoans, with a retractable lophophore and U-shaped digestive tract. They are widely distributed and highly diverse in extant marine and freshwater environments. Current confident fossils of the earliest bryozoan only occur in the Early Ordovician, although molecular estimation date their origin in or prior to the early Cambrian, rendering the origin and early evolution of bryozoans are intensely debated. Here, we describe two cyclostomes, Panpipora yunnanensis gen. et. sp. nov. and Corynotrypa sp., having been recovered from the Cambrian Chengjiang Biota (~ 518 m.y.) in Southwest China. The bryozoans represent the earliest fossils of Bryozoa, predating the record of the phylum by more than 30 million years. Our finding reveals that the Bryozoa, as all other skeletonised metazoans, first evolved during the Cambrian Explosion, and it is congruent with estimation of molecular clock that the cyclostomes is the earliest biomineralised clade. Corynotrypa might be derived from unmineralized ctenostomes by stolonal mineralization and change of growth direction of polypides from vertical to creeping. The unmineralised frontal exterior wall might be a share character existed in all ancestral clades. Encrusting specimens that inhabited in muddy environments have been confirmed here, further suggesting that encrusting bryozoans underwent a profound ecological migration from soft- to hard-bottom facies from Cambrian to Ordovician.

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The Burgess Shale arthropod Mollisonia (M. sinica new species): new occurrence from the Middle Cambrian Kaili fauna of southwest China

Journal of Paleontology ◽

10.1017/s0022336000057917 ◽

2002 ◽

Vol 76 (6) ◽

pp. 1106-1108 ◽

Cited By ~ 9

Author(s):

Xingliang Zhang ◽

Yuanlong Zhao ◽

Ruidong Yang ◽

Degan Shu

Keyword(s):

Southwest China ◽

Middle Part ◽

Guizhou Province ◽

Cambrian Explosion ◽

Early Cambrian ◽

Burgess Shale ◽

Middle Cambrian ◽

Lowermost Part ◽

Dark Green ◽

Chengjiang Lagerstätte

The Early Cambrian Chengjiang Lagerstätte, Yunnan Province, Southwest China, has become one of the most celebrated Cambrian fossil Lagerstatten not only for perhaps the earliest biota of soft-bodied organisms in the Phanerozoic (Yuan and Zhao, 1999; Zhang et aI., 2001; but see Budd and Jensen, 2000), but also for a number of significant discoveries (Shu et al., 1996a, 1996b, 1999a, 1999b, 2001), proven to be of particular importance for our understanding the Cambrian explosion. Also in Southwest China, Guizhou Province, there is a very significant, although less acclaimed, Middle Cambrian soft-bodied fauna as well, namely the Kaili fauna, which occurs in the Kaili Formation in Kaili area (Kuizhou). The age of the Kaili Formation ranges from late Early to early Middle Cambrian. Regionally, the Kaili Formation is about 222 m thick and consists of three parts. The lowermost part (late Early Cambrian, about 55 m thick) is dominated by thin, calcareous siltstone strata interbedded with limestone layers at the base. The middle part (early Middle Cambrian, ca. 123 m) consists of dark green mudstone and shale, while the uppermost part (ca. 44 m) is composed of interbedded limestone and silty shale. The Kaili fauna is derived from mudstones in the middle part of the formation (Zhao et aI., 1994; Zhu et aI., 2000).

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New vauxiid sponges from the Chengjiang Biota and their evolutionary significance

Journal of the Geological Society ◽

10.1144/jgs2020-162 ◽

2021 ◽

pp. jgs2020-162

Author(s):

Fan Wei ◽

Yang Zhao ◽

Ailin Chen ◽

Xianguang Hou ◽

Peiyun Cong

Keyword(s):

South China ◽

Vertical Surface ◽

Cambrian Explosion ◽

Evolutionary Significance ◽

Early Cambrian ◽

Geological History ◽

Burgess Shale ◽

Content Type ◽

Dermal Layer ◽

Chengjiang Biota

Aspiculate demosponges are rarely described in geological history on account of the absence of spicules that are stable and resistant to degradation. One exception is the exquisite preservation of sponges without any mineralised skeletons discovered in Lagerstätten (e.g. the Burgess Shale). The Chengjiang Biota, an early example of a Burgess Shale-type Biota in South China (Cambrian Series 2, Stage 3), is one of the only examples of convincing aspiculate sponges until now. Here, we describe Vauxia pregracilenta sp. nov. and V. paraleioia sp. nov., as well as two poorly preserved vauxiid specimens (Vauxia sp.) in open nomenclature, from the Chengjiang Biota. V. pregracilenta has a fan-like holdfast and branches in various sizes, as well as a typical two-layered net-like skeleton, without spicules. The endosomal layer is hexagonal, while the dermal layer is sub-rectangular. V. paraleioia is characterised by a two-layered subconical skeleton, with the dermal layer ornamented with vertical surface grooves. The openings of the dermal and endosomal layers of V. paraleioia are both hexagonal but of different sizes. These newly discovered Vauxia species indicate that the aspiculate sponges were diversified in the early Cambrian period. Partial silicification of the fibres of aspiculate Vauxia are confirmed from the Chengjiang Biota.Thematic collection: This article is part of the Advances in the Cambrian Explosion collection available at: https://www.lyellcollection.org/cc/advances-cambrian-explosion

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Tabelliscolex (Cricocosmiidae: Palaeoscolecidomorpha) from the early Cambrian Chengjiang Biota, and the evolution of seriation in Ecdysozoa

Journal of the Geological Society ◽

10.1144/jgs2021-060 ◽

2021 ◽

pp. jgs2021-060

Author(s):

Xiaomei Shi ◽

Richard J. Howard ◽

Gregory D. Edgecombe ◽

Xianguang Hou ◽

Xiaoya Ma

Keyword(s):

Phylogenetic Analyses ◽

Sensu Stricto ◽

Cambrian Explosion ◽

Early Cambrian ◽

Content Type ◽

Link Type ◽

Stem Group ◽

New Material ◽

Supplementary Material ◽

Chengjiang Biota

Cricocosmiidae is a clade of palaeoscolecid-like worms from the Chengjiang Biota, China (Cambrian Stage 3). In contrast to palaeoscolecids sensu stricto, which exhibit tessellating micro-plate trunk ornamentation, cricocosmiids possess larger, serially repeated sets of trunk sclerites bearing resemblance to lobopodian trunk sclerites (e.g., Microdictyon spp.). Cricocosmiidae were therefore proposed as stem-group Panarthropoda in some studies but are recovered as stem-group Priapulida in most phylogenetic analyses. The affinity of cricoscosmiids within Ecdysozoa is therefore of much interest, as is testing the homology of these seriated structures. We report four new specimens of the rare cricocosmiid Tabelliscolex hexagonus, yielding new details of the ventral trunk projections, sclerites and proboscis. New data confirm T. hexagonus possessed paired ventral trunk projections in a consistent seriated pattern, which is also reported from new material of Cricocosmia jinningensis (Cricocosmiidae) and Mafangscolex yunnanensis (Palaeoscolecida sensu stricto). Even when the seriated sclerites and ventral projections of cricocosmiids are coded as homologous with the seriated trunk sclerites and paired appendages, respectively, of lobopodian panarthropods, our tree searches indicate they are convergent. Cricocosmiidae is nested within a monophyletic “Palaeoscolecida sensu lato” clade (Palaeoscolecidomorpha nov.) in stem-group Priapulida. Our study indicates that morphological seriation has independent origins in Scalidophora and Panarthropoda.Thematic collection: This article is part of the Advances in the Cambrian Explosion collection available at: https://www.lyellcollection.org/cc/advances-cambrian-explosionSupplementary material:https://doi.org/10.6084/m9.figshare.c.5551565

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Symbiotic fouling of Vetulicola, an early Cambrian nektonic animal

Communications Biology ◽

10.1038/s42003-020-01244-1 ◽

2020 ◽

Vol 3 (1) ◽

Author(s):

Yujing Li ◽

Mark Williams ◽

Thomas H. P. Harvey ◽

Fan Wei ◽

Yang Zhao ◽

...

Keyword(s):

Fossil Record ◽

Yunnan Province ◽

Southwest China ◽

Early Cambrian ◽

Chengjiang Biota ◽

Marine Deposit

Abstract Here, we report the earliest fossil record to our knowledge of surface fouling by aggregates of small vermiform, encrusting and annulated tubular organisms associated with a mobile, nektonic host, the enigmatic Cambrian animal Vetulicola. Our material is from the exceptionally preserved early Cambrian (Epoch 2, Age 3), Chengjiang biota of Yunnan Province, southwest China, a circa 518 million-year old marine deposit. Our data show that symbiotic fouling relationships between species formed a component of the diversification of animal-rich ecosystems near the beginning of the Phanerozoic Eon, suggesting an early escalation of intimate ecologies as part of the Cambrian animal radiation.

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Intraspecific variation in the Cambrian: new observations on the morphology of the Chengjiang euarthropod Sinoburius lunaris

BMC Ecology and Evolution ◽

10.1186/s12862-021-01854-1 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Michel Schmidt ◽

Yu Liu ◽

Xianguang Hou ◽

Joachim T. Haug ◽

Carolin Haug ◽

...

Keyword(s):

Intraspecific Variation ◽

Southwest China ◽

3D Models ◽

Morphological Characters ◽

Open Questions ◽

New Findings ◽

Unique Shape ◽

Variable Species ◽

Chengjiang Biota ◽

3D Software

Abstract Background The Chengjiang biota from southwest China (518-million-years old, early Cambrian) has yielded nearly 300 species, of which more than 80 species represent early chelicerates, crustaceans and relatives. The application of µCT-techniques combined with 3D software (e.g., Drishti), has been shown to be a powerful tool in revealing and analyzing 3D features of the Chengjiang euarthropods. In order to address several open questions that remained from previous studies on the morphology of the xandarellid euarthropod Sinoburius lunaris, we reinvestigated the µCT data with Amira to obtain a different approach of visualization and to generate new volume-rendered models. Furthermore, we used Blender to design 3D models showing aspects of intraspecific variation. Results New findings are: (1) antennulae consist of additional proximal articles that have not been detected before; (2) compared to other appendages, the second post-antennular appendage has a unique shape, and its endopod is comprised of only five articles (instead of seven); (3) the pygidium bears four pairs of appendages which are observed in all specimens. On the other hand, differences between specimens also have been detected. These include the presence/absence of diplotergites resulting in different numbers of post-antennular appendages and tergites and different distances between the tip of the hypostome and the anterior margin of the head shield. Conclusions Those new observations reveal intraspecific variation among Chengjiang euarthropods not observed before and encourage considerations about possible sexual dimorphic pairs or ontogenetic stages. Sinoburius lunaris is a variable species with respect to its morphological characters, cautioning that taxon-specific variabilities need to be considered when exploring new species.

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Current understanding on the Cambrian Explosion: questions and answers

PalZ ◽

10.1007/s12542-021-00568-5 ◽

2021 ◽

Author(s):

Xingliang Zhang ◽

Degan Shu

Keyword(s):

Environmental Changes ◽

Size Variation ◽

Progressive Increase ◽

Cambrian Explosion ◽

Time Interval ◽

Early Cambrian ◽

Ecological Processes ◽

Questions And Answers ◽

Evolutionary Event ◽

History Of

AbstractThe Cambrian Explosion by nature is a three-phased explosion of animal body plans alongside episodic biomineralization, pulsed change of generic diversity, body size variation, and progressive increase of ecosystem complexity. The Cambrian was a time of crown groups nested by numbers of stem groups with a high-rank taxonomy of Linnaean system (classes and above). Some stem groups temporarily succeeded while others were ephemeral and underrepresented by few taxa. The high number of stem groups in the early history of animals is a major reason for morphological gaps across phyla that we see today. Most phylum-level clades achieved their maximal disparity (or morphological breadth) during the time interval close to their first appearance in the fossil record during the early Cambrian, whereas others, principally arthropods and chordates, exhibit a progressive exploration of morphospace in subsequent Phanerozoic. The overall envelope of metazoan morphospace occupation was already broad in the early Cambrian though it did not reach maximal disparity nor has diminished significantly as a consequence of extinction since the Cambrian. Intrinsic and extrinsic causes were extensively discussed but they are merely prerequisites for the Cambrian Explosion. Without the molecular evolution, there could be no Cambrian Explosion. However, the developmental system is alone insufficient to explain Cambrian Explosion. Time-equivalent environmental changes were often considered as extrinsic causes, but the time coincidence is also insufficient to establish causality. Like any other evolutionary event, it is the ecology that make the Cambrian Explosion possible though ecological processes failed to cause a burst of new body plans in the subsequent evolutionary radiations. The Cambrian Explosion is a polythetic event in natural history and manifested in many aspects. No simple, single cause can explain the entire phenomenon.

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Decoupled evolution of soft and hard substrate communities during the Cambrian Explosion and Great Ordovician Biodiversification Event

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1523087113 ◽

2016 ◽

Vol 113 (25) ◽

pp. 6945-6948 ◽

Cited By ~ 45

Author(s):

Luis A. Buatois ◽

Maria G. Mángano ◽

Ricardo A. Olea ◽

Mark A. Wilson

Keyword(s):

Late Ordovician ◽

Hard Substrate ◽

Cambrian Explosion ◽

Early Cambrian ◽

Continuous Increase ◽

Late Cambrian ◽

Unconsolidated Sediment ◽

Underlying Causes ◽

Hard Substrates ◽

Shed Light

Contrasts between the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE) have long been recognized. Whereas the vast majority of body plans were established as a result of the CE, taxonomic increases during the GOBE were manifested at lower taxonomic levels. Assessing changes of ichnodiversity and ichnodisparity as a result of these two evolutionary events may shed light on the dynamics of both radiations. The early Cambrian (series 1 and 2) displayed a dramatic increase in ichnodiversity and ichnodisparity in softground communities. In contrast to this evolutionary explosion in bioturbation structures, only a few Cambrian bioerosion structures are known. After the middle to late Cambrian diversity plateau, ichnodiversity in softground communities shows a continuous increase during the Ordovician in both shallow- and deep-marine environments. This Ordovician increase in bioturbation diversity was not paralleled by an equally significant increase in ichnodisparity as it was during the CE. However, hard substrate communities were significantly different during the GOBE, with an increase in ichnodiversity and ichnodisparity. Innovations in macrobioerosion clearly lagged behind animal–substrate interactions in unconsolidated sediment. The underlying causes of this evolutionary decoupling are unclear but may have involved three interrelated factors: (i) a Middle to Late Ordovician increase in available hard substrates for bioerosion, (ii) increased predation, and (iii) higher energetic requirements for bioerosion compared with bioturbation.

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Brachiopod-dominated communities and depositional environment of the Guanshan Konservat-Lagerstätte, eastern Yunnan, China

Journal of the Geological Society ◽

10.1144/jgs2020-043 ◽

2020 ◽

Vol 178 (1) ◽

pp. jgs2020-043 ◽

Cited By ~ 1

Author(s):

Feiyang Chen ◽

Glenn A. Brock ◽

Zhiliang Zhang ◽

Brittany Laing ◽

Xinyi Ren ◽

...

Keyword(s):

Depositional Environment ◽

Sedimentary Environment ◽

Low Energy ◽

Cambrian Explosion ◽

Early Cambrian ◽

Tissue Preservation ◽

Content Type ◽

Guanshan Biota ◽

Supplementary Material ◽

Later Phase

The Guanshan Biota is an unusual early Cambrian Konservat-Lagerstätte from China and is distinguished from all other exceptionally preserved Cambrian biotas by the dominance of brachiopods and a relatively shallow depositional environment. However, the faunal composition, overturn and sedimentology associated with the Guanshan Biota are poorly understood. This study, based on collections through the best-exposed succession of the basal Wulongqing Formation at the Shijiangjun section, Wuding County, eastern Yunnan, China recovered six major animal groups with soft tissue preservation; brachiopods vastly outnumbered all other groups. Brachiopods quickly replace arthropods as the dominant fauna following a transgression at the base of the Wulongqing Formation. A transition from a botsfordiid-, eoobolid- and acrotretid- to an acrotheloid-dominated brachiopod assemblage occurs up-section. Four episodically repeated lithofacies reveal a relatively low-energy, offshore to lower shoreface sedimentary environment at the Shijiangjun section, which is very different from the Wulongqing Formation in the Malong and Kunming areas. Multiple event flows and rapid obrution are responsible for faunal overturn and fluctuation through the section. A detailed lithofacies and palaeontological investigation of this section provides a better understanding of the processes and drivers of faunal overturn during the later phase of the Cambrian Explosion.Supplementary material: Composition and comparison of the Malong Fauna and the Guanshan Biota is are available at: https://doi.org/10.6084/m9.figshare.c.5080799

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Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan

BMC Evolutionary Biology ◽

10.1186/s12862-020-01720-6 ◽

2020 ◽

Vol 20 (1) ◽

Author(s):

Richard J. Howard ◽

Gregory D. Edgecombe ◽

Xiaomei Shi ◽

Xianguang Hou ◽

Xiaoya Ma

Keyword(s):

Feeding Strategy ◽

Phylogenetic Analyses ◽

Morphological Diversity ◽

Early Cambrian ◽

Ancestral State ◽

Crown Group ◽

Stem Group ◽

Chengjiang Biota ◽

Fossil Records ◽

Experimental Decay

Abstract Background Ecdysozoa are the moulting protostomes, including arthropods, tardigrades, and nematodes. Both the molecular and fossil records indicate that Ecdysozoa is an ancient group originating in the terminal Proterozoic, and exceptional fossil biotas show their dominance and diversity at the beginning of the Phanerozoic. However, the nature of the ecdysozoan common ancestor has been difficult to ascertain due to the extreme morphological diversity of extant Ecdysozoa, and the lack of early diverging taxa in ancient fossil biotas. Results Here we re-describe Acosmia maotiania from the early Cambrian Chengjiang Biota of Yunnan Province, China and assign it to stem group Ecdysozoa. Acosmia features a two-part body, with an anterior proboscis bearing a terminal mouth and muscular pharynx, and a posterior annulated trunk with a through gut. Morphological phylogenetic analyses of the protostomes using parsimony, maximum likelihood and Bayesian inference, with coding informed by published experimental decay studies, each placed Acosmia as sister taxon to Cycloneuralia + Panarthropoda—i.e. stem group Ecdysozoa. Ancestral state probabilities were calculated for key ecdysozoan nodes, in order to test characters inferred from fossils to be ancestral for Ecdysozoa. Results support an ancestor of crown group ecdysozoans sharing an annulated vermiform body with a terminal mouth like Acosmia, but also possessing the pharyngeal armature and circumoral structures characteristic of Cambrian cycloneuralians and lobopodians. Conclusions Acosmia is the first taxon placed in the ecdysozoan stem group and provides a constraint to test hypotheses on the early evolution of Ecdysozoa. Our study suggests acquisition of pharyngeal armature, and therefore a change in feeding strategy (e.g. predation), may have characterised the origin and radiation of crown group ecdysozoans from Acosmia-like ancestors.

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