Cambrian Fortunian Stage Research Articles

Growth patterns and affinities of Huizenodus oligaspinosus (?Cnidaria) from the lower Cambrian of South China

Helmet-like small shelly fossils from the Cambrian Fortunian Stage of South China are a class of morphological taxa with uncertain affinities. Here, we redefine the genera Amoebinella and Huizenodus and consider Huizenodus oligaspinosus to be a senior synonym of Amoebinella echinata. In addition, we report two compound fossils of H. oligaspinosus for the first time from the Fortunian Zhangjiagou Lagerstätte in southern Shaanxi. Their multi-branched, dendritic, rigid structure is similar to the skeletons in several groups of colonial anthozoans, and thus, H. oligaspinosus may represent the skeletal structure of an ancestral anthozoan. H. oligaspinosus could have further constructed its skeleton by producing secondary individuals from the main branches or the sub-branches of the primary individuals to accommodate more polyps.

AGE CONSTRAINTS AND SOURCE AREAS FOR THE PRECAMBRIAN TO CAMBRIAN STRATA OF THE SOUTHERN YENISEI RIDGE (REDKOLESNAYA AND OSTROVNOY FORMATIONS)

The Precambrian to Cambrian strata at the southwestern margin of the Siberian Platform are ubiquitously characterized by a gradual transition from red-colored alluvial and deltaic deposits to shallow-marine carbonates, reflecting a transgressive infill of the accommodation space of the foreland basin. However, a supposed synchronicity of the Early Precambrian marine transgressive events calls for verification by geochronological and bio- and chemostratigraphic dating. The herein-presented data on small skeletal fossils, trace fossils and variations in the carbon isotope composition of carbonates from the mixed carbonate-terrigenous succession (Redkolesnaya and Ostrovnoy formations) in the southern Yenisei ridge show that the base of the Cambrian Fortunian stage is placed within the Redkolesnaya formation. Age distribution of detrital zircons in the studied succession suggests the Siberian craton to be a major source of the clastic material in the foreland basin during the development of the Redkolesnaya formation. An increase in the amount of zircons derived from "non-Siberian" sources, located at the southwestern periphery of the paleocontinent at that time, in the coeval strata of the northern part of the southern Yenisei ridge, indicates a complex morphology of the paleobasin and considerable differentiation among the sources of clastic material therein.

New Qinscyphus material from the Fortunian of South China

Microscopic medusozoans from the Cambrian Fortunian stage of South China are well known for their exceptionally preserved embryos and elongated tubes. However, additional details of their morphology remain unclear. This paper describes new medusozoan fossils showing the whole apical complement and covering the morphological integrity of Qinscyphus. The apical part of Qinscyphus is considered to be soft during early ontogeny, and the inverted pentagonal pyramid may gradually form with growth and development. This discovery of the apical complement of Qinscyphus is novel and essential to complement the external morphology of early medusozoan fossils. More importantly, the new specimens have different annuli with triangular thickenings, providing a more comprehensive view on the developmental sequence of Qinscyphus. Therefore, this work allows a better understanding of early medusozoans ecology and evolution.

A new species of Decimoconularia (Cnidaria, Medusozoa) from the Lower Cambrian of South China

Hexangulaconulariids, a family of biradially symmetrical medusozoan cnidarians, have been widely reported from the Lower Cambrian of South China. The four currently recognized genera of hexangulaconulariids differ from each other mainly in the number of faces in the abapical region of the periderm. However, previously published illustrations of the monospecific type genus, Hexangulaconularia, clearly show two distinct morphotypes, one with six faces and the other with 10. Specimens with 10 faces are herein reassigned to the genus Decimoconularia. In addition, the new species D. anisfacialis is described from the Kuanchuanpu Formation (Cambrian Fortunian Stage) in the Kuanchuanpu and Shizhonggou sections in Ningqiang County, southern Shaanxi Province, China. Also described are additional specimens of H. formosa from the same formation in the Zhangjiagou section in Xixiang County, southern Shaanxi Province, and from Member 2 of the Yanjiahe Formation (Cambrian Fortunian Stage) in western Hubei Province. The discovery of D. anisfacialis extends the known stratigraphical range of Decimoconularia, now composed of two species, downward from Cambrian Stage 2 into the Fortunian Stage. Additionally, certain specimens previously assigned to H. formosa are reassigned to D. anisfacialis. The diagnoses of Hexangulaconularia, Decimoconularia, and Hexangulaconulariidae are emended accordingly. In accordance with the rule of time priority, the previously designated type genus and species, Hexaconularia He and Yang, 1986 and Hexaconularia sichuanensis He and Yang, 1986, are replaced herein by Hexangulaconularia He, in Xing et al., 1983.

Cochleatina: an enigmatic Ediacaran–Cambrian survivor among small carbonaceous fossils (SCFs)

AbstractConspicuously few body‐fossil taxa are known to span the Ediacaran–Cambrian boundary, a pattern usually taken to signal either a terminal Proterozoic mass extinction, or taphonomic failure. We draw attention to the emerging record of small carbonaceous fossils (SCFs), which exhibit continuous preservation spanning this critical interval. Here we focus on the enigmatic SCF Cochleatina, a morphologically complex coil‐shaped problematicum that ranges across the Ediacaran–Cambrian divide, and is potentially among the oldest fossil occurrences of metazoans. We report new material of Cochleatina canilovica from the Ediacaran of Estonia and Ukraine, which offers new characters for assessing its palaeobiology. Significantly, new specimens include sets of three‐alike triplets of Cochleatina adhering to organic sheets, suggesting a clustering habit, or grouping of elements within an individual during life; an important step in constraining the morphology and ecology of this Ediacaran–Cambrian problematicum. We present revised systematic descriptions for Cochleatina and C. canilovica, and critically evaluate previous biological interpretations, drawing comparisons with metazoan, algal and protistan analogues. We reject hypotheses supporting Cochleatina as a metazoan mouthpart, and suggest new grounds for viewing Cochleatina as a potential multicomponent predator that trapped protists among microbial mats. Most occurrences are from Baltica, but we synthesize sporadic reports of Cochleatina from other palaeocontinents, pointing to its global distribution during the latest ˜10 myr of the Ediacaran and majority of the earliest Cambrian Fortunian Stage. As a rare example of an ‘Ediacaran survivor’, Cochleatina highlights the broader significance of SCFs as a novel means of tracking evolutionary patterns through the Proterozoic–Phanerozoic transition.

A new scalidophoran animal from the Cambrian Fortunian Stage of South China and its implications for the origin and early evolution of Kinorhyncha

Kinorhyncha is a cycloneuralian phylum with about 240 extant species, and it was not until 2015 that the first and only fossil kinorhynch species Eokinorhynchus rarus was reported. Here, we describe a new scalidophoran animal, Zhongpingscolex qinensis gen. et sp. nov., from the Cambrian Fortunian Kuanchuanpu Formation at Zhangjiagou section, southern Shaanxi Province, South China. The holotype and only specimen possesses morphology comparable to that of E. rarus. They both possess heterogeneous trunk annuli, and compared with E. rarus, Z. qinensis gen. et sp. nov. lacks a neck. Phylogenetic analysis resolves Z. qinensis gen. et sp. nov. as the sister group of E. rarus, both constituting stem-lineage derivatives of Kinorhyncha. The evolutionary scenario from the last common ancestor of crown-group Scalidophora to the last common ancestor of total-group Kinorhyncha includes the acquisition of a much shortened body with a relatively low body length to width ratio, heterogeneous trunk annuli, and macroannuli with simple armatures. The spines, large spinose sclerites, and annular rings of rectangular plates are autapomorphic to E. rarus, and segments (zonites) with independent cuticular plates as in crown-group kinorhynchs were evolved later.

New macrobenthic cycloneuralians from the Fortunian (lowermost Cambrian) of South China

Although morphology-based phylogenetic analyses and molecular data suggested that the cycloneuralians might have emerged in the Ediacaran Period, the oldest known fossil remains of cycloneuralians were first reported from the Cambrian Fortunian Stage of South China, and to date four genera and species as well as nine indeterminate forms have been described. Here, we report the latest discoveries of cycloneuralians from the Fortunian Kuanchuanpu Formation at Zhangjiagou Lagerstätte, Dahe Village, Xixiang County, southern Shaanxi Province, South China. A new genus and species Dahescolex kuanchuanpuensis n. gen. n. sp. is described, and a previously reported genus and species Eopriapulites sphinx is re-described. Dahescolex kuanchuanpuensis n. gen. n. sp. is suggested to be a stem-lineage derivative of Scalidophora, whereas E. sphinx may represent a stem-lineage derivative of Cycloneuralia. From the fragments discovered, the new specimens are suggested to have reached millimeters in dimension, and the original individuals are estimated to have dimensions in centimeter, hence falls within the size range of macrobenthos. Therefore, at least some of the Fortunian cycloneuralians can be considered macrobenthic, and it is suggested here that the Cycloneuralia may have originated in the Fortunian macrobenthos.

New armoured scalidophorans (Ecdysozoa, Cycloneuralia) from the Cambrian Fortunian Zhangjiagou Lagerstätte, South China

AbstractAlthough molecular studies estimated that cycloneuralians might have originated in the Ediacaran Period and diversified in the early Cambrian, it was not until 2014 that they were first reported from the Cambrian Fortunian Stage. To date only two species and five indeterminate forms have been described. Here, we report new three‐dimensionally phosphatized microfossils of cycloneuralians from the Fortunian Zhangjiagou Lagerstätte, South China. Two new genera and species, Qinscolex spinosus gen. et sp. nov. and Shanscolex decorus gen. et sp. nov., and Indeterminate Forms 1–7 are described and tentatively assigned to total‐group Scalidophora, greatly increasing the diversity of the Fortunian cycloneuralians. These Fortunian cycloneuralians have diverse cuticular spines, plates, and spinose sclerites of various sizes on the trunk, thus assignment of co‐occurring fragmented trunk parts or disassociated spines or sclerites to a specific species is currently impossible. Some of the Fortunian cycloneuralians might have reached a centimetre in length; they may have been temporary meiobenthos in their juvenile or younger adult stages, only joining the macrobenthos when they reached macroscopic dimensions. It is proposed that an introvert with hexaradially symmetric and internally hollow scalids might be the plesiomorphic state for cycloneuralians.

New material of scalidophoran worms in Orsten-type preservation from the Cambrian Fortunian Stage of South China

AbstractScalidophoran worms diversified in the Cambrian Fortunian, as indicated by recent reports from this stage, with two described species and two more unnamed forms exclusively from Orsten-type Lagerstätten yielding three-dimensionally phosphatized fossils. Here, we report new material of scalidophoran worms in Orsten-type preservation from the Cambrian Fortunian Xinli section in northern Sichuan Province, South China. At least five forms of scalidophoran worms were recovered from this location, includingEokinorhynchus rarusZhang et al., 2015 and four unnamed taxa—Forms A, B, C, and D. Co-occurring disassociated spinose small shelly fossils might also be isolated cuticular elements of these early scalidophoran worms. The ontogeny ofEokinorhynchus rarusis revised. Forms A, C, and D are assigned to total-group Scalidophora to indicate their uncertain positions within Scalidophora, while Form B might be a close relative ofEokinorhynchus rarus. The current work highlights the significance of Orsten-type Lagerstätten in uncovering the morphology, ontogeny, and taxonomy of early Scalidophora and Cycloneuralia, made particularly available by the new finds in China.

A new scyphozoan from the Cambrian Fortunian Stage of South China

AbstractAnimals with radial symmetry are abundant in the Cambrian Fortunian Stage of South China, but with relatively low diversity: representatives include Olivooides, Quadrapyrgites, carinachitiids, hexangulaconulariids and Pseudooides. Here, we report a new radial animal, Qinscyphus necopinus gen. et sp. nov., from the Fortunian small shelly fauna of southern Shaanxi Province, South China. Qinscyphus necopinus has a cup‐shaped profile, with slightly raised annuli and five groups of triangular thickenings in pentaradial symmetry. This organism has a comparable morphology to, and thus a close affinity with, Olivooides and Quadrapyrgites, and is interpreted as a coronate scyphozoan. This discovery adds a new crown‐group cnidarian to the Cambrian Explosion.

New Maikhanellid Shells and Siphogonuchitid Spicule Bundles from the Cambrian Fortunian Stage of South China

AbstractMaikhanellids are a distinct group of Cambrian Fortunian small shelly fossils by the cap‐shaped profiles and scaly shell ornamentation. According to the individual shell shape and ornamentation feature types of SO maikhanellids fossils which were collected from Xixiang botia, we confirmed the family Maikhanellidae content of six genera, which are Maikhanella, Ramenta, Purella, Ramentoides, Yunnannopleura and Mediata. Unlike the halkieriid animals whose shells and spicules are articulated on different body parts, maikhanellids were presumably yielded by siphogonuchitid spicules penetrating the intermediate matrix (the “spicule shell” hypothesis), and this is the reason that some researchers treated maikhanellids and co‐occurring siphogonuchitids as synonyms. The affinities of Maikhanellids and siphogonuchitids remain debatable. Here, we report three dimensionally phosphatized maikhanellid shells and siphogonuchitid spicule bundles from the Cambrian Fortunian small shell faunas of South China. They differ from all the previously reported maikhanellids and siphogonuchitids, and may represent new types. The intact and smooth surface underneath the partially preserved scales of the shells challenges the “spicule‐shell” hypothesis. The present siphogonuchitid spicules differ from the maikhanellid scales in size, morphology, and arrangement pattern, thus the spicules might not be derived from the shells. Whether the shells and spicule bundles were articulated on different body parts of the same animals remains unknown.

Secondary phosphatization of the earliest Cambrian small shelly fossil Anabarites from southern Shaanxi

Biomineralization may have an extremely long evolutionary history since the Paleoarchean, while the widespread biomineralization among metazoan lineages started at the earliest Cambrian. However, the primary mineralogy of Anabarites shell remains controversial. Optical microscopic observations combined with the Back-Scattered Electron (BSE) and Energy-Dispersive X-ray Spectroscopy (EDS) analyses are used to study the shell of the fossil Anabarites from the Kuanchuanpu fauna in southern Shaanxi Province in China, which is correlated to the Cambrian Fortunian Stage. The EDS analysis shows that the phosphorus-rich layer closely adjacent to the calcified layer exhibits a Ca: P: C ratio compositionally similar to the mineral fluorapatite (Ca5(PO4,CO3)3(F,CO3). The result that the calcified layer and the phosphorus-rich layer have different chemical compositions is consistent with the optical observation that there is an obvious gap between these two layers and the phosphorus-rich layer can extend to the phosphatic material inside of the tube, suggesting the phosphorus-rich layer doesn’t belong to the original shell. We suggest that the phosphorous-rich layer is diagenetic in origin, precipitated as a result of phosphorus release during the decay of organic matter by microbes. Considering the outermost shell layer (OMS, biologically controlled carbonate shell layer) should display different isotopic information from the carbonate matrix (i.e., OMS is 12C concentrated due to the biogenic organic matter template is readily rich in 12C), NanoSIMS was used to map ion distributions of C and N in the shell of Anabarites and matrix. However, ion images show that the concentration differences of 12C, 13C and 26CN among the OMS and the matrix are unclear, while 12C and 26CN are supposed to be enriched in the OMS. Therefore, the minor isotopic differences between the shell and the matrix is hard to be detected by NanoSIMS, at least in our sample, probably due to alteration of the 12C-rich characteristic of the Anabarites OMS during the late diagenesis.

The earliest pelagic jellyfish with rhopalia from Cambrian Chengjiang Lagerstätte

Modern cnidarian medusae generally show a triphasic life cycle with the succession of a larva, a sessile polyp and a pelagic medusa stage. The debate around the metagenesis of sessile polyps into pelagic medusae has lasted for more than 100years. When pelagic forms originated is not clear. Hitherto, the earliest crown-group medusae have been found at Cambrian Stage 5 (traditional Middle Cambrian, 509Ma) in Utah, while diverse stem-group medusozoans were found in the basal Cambrian Fortunian Stage. No reliable medusae have been found from Cambrian Series 2 Stage 3 (ca. 521Ma), although the marine benthic community teemed with many phyla of bilaterians, sponges and ctenophores. Here, we reinterpret Yunnanoascus haikouensisHu et al. (2007), originally described as a ctenophore, as a pelagic, predatory, crown-group medusozoan, based on the presence of rhopalia, possible radial canals and marginal tentacles. The medusae were a predatory member of the pelagic food web at the middle level of the ocean at Cambrian Stage 3.

Review of Research on Early Cambrian Phosphatized Quadrapyrgites

AbstractThe metazoan Quadrapyrgites consists, from proximal to distal ends, of an oral area, a cone, a collar, and an apex from the Early Cambrian Fortunian Stage in Xixiang Zhangjiagou section, southern Shaanxi Province, South China. Three morphological types of the apex, the most characteristic feature of the taxon, are identified from hundreds of Quadrapyrgites specimens. The Quadrapyrgites growth zone is situated at the oral end, where 12 terminal lobes are generated, uplifted, enlarged, and evaginated to form a crest; A one‐by‐one of crest number from 2 to 13 has been recognized. The unique growth pattern and ontogenetic sequence refute a cubozoan or cycloneuralian affinity for Olivooides and Quadrapyrgites, and instead defend a coronate scyphozoan hypothesis. An embryonic development and ontogenetic sequence with embryo and crest is constructed.

New material of the oldest known scalidophoran animal Eopriapulites sphinx

Eopriapulites sphinx is the oldest known scalidophoran animal and so far the only cycloneuralian body fossil from the Cambrian Fortunian Stage. The hexaradial symmetry exhibited by the arrangement of its pharyngeal teeth, coronal scalids and introvert scalids expand our knowledge on the early evolution of cycloneuralians. The holotype and only specimen is a fragment with the proboscis and the anterior trunk part preserved, but the posterior trunk part is missing. Here, we report three-dimensionally phosphatized worm trunk fragments from the same locality and horizon yielding E. sphinx. They are regarded as conspecific with E. sphinx based on co-occurrence and identical annulations, and provide key information on the trunk morphology. E. sphinx is completely reconstructed here as a long vermiform animal with densely annulated trunk and no caudal outgrowths. An updated phylogenetic analysis supports that E. sphinx is a stem-lineage derivative of Scalidophora and also indicates that the hexaradial symmetry of Eopriapulites might have evolved independently from that of Nematoida.

Marine redox variations and nitrogen cycle of the early Cambrian southern margin of the Yangtze Platform, South China: Evidence from nitrogen and organic carbon isotopes

The early Cambrian is a crucial interval, during which the marine environment encountered significant perturbations alongside key biological innovations. The nitrogen isotopic composition of ancient sediments has the potential to record co-variation between the marine ecosystem and environmental conditions. Here we report bulk nitrogen and organic carbon isotopic compositions accompanied by Mo concentration data (a proxy for redox conditions) for a shelf marginal drill core section (Sancha) and a deep basinal outcrop section (Yuanjia) in Hunan province, South China.For the Cambrian Fortunian Stage, variable δ15Nbulk values (−4 to +2‰) and low δ13Corg values (−35‰ to −33‰) from the Yuanjia section indicate that anoxic waters shoaled into the photic zone, with ammonia assimilation competing with anammox in the basinal area. In the late Cambrian Stage 2, low δ15Nbulk and δ13Corg values, together with high Mobulk concentrations (δ15Nbulk=−5 to 0‰; δ13Corg=−33.5 to −31.0‰; >100ppm Mobulk in Sancha section and δ15Nbulk=∼0‰; δ13Corg=∼−33‰ >100ppm Mobulk in Yuanjia section), reflect intense N2-fixation accompanied by intermittent ammonia assimilation under expanded euxinic condition with shoaling chemocline possibly into the photic zone. In the early Cambrian Stage 3, relatively high δ15Nbulk values, alongside positive δ13Corg excursions, at both sections indicate an increasing contribution from 15N-enriched nitrate assimilation and hence more oxic conditions. Shelf margin sediments from the middle and late parts of Cambrian Stage 3 are characterized by low δ15Nbulk values (∼0‰), being lowest in the basinal area (−3 to 0‰). In combination with high Mobulk concentration (>100ppm) and high Mo/TOCbulk ratios (averaging ∼18) in deep basinal sediments, these data suggest that the photic zone became anoxic again, but that sulfidic conditions occurred in the basinal area only. Compared with Stage 2, euxinia was less extensive during this interval, with photosynthetic biomass dominating over chemoautotrophic biomass at both localities.Based on a combination of δ15N data from this study and published data from studies on contemporaneous sections in Yunnan Province and the Three Gorges area, it is possible to reconstruct the spatial variability and temporal evolution of redox conditions in the various marine environments along the southern margin of the Yangtze platform. The basinal area appears to have been dominated by anoxia and intermittent euxinia in the photic zone during most of the early Cambrian (Fortunian Stage to Stage 3) with the exception of more oxic conditions during early Stage 3. On the platform, oxygenated shallow water prevailed with the exception of the notable Cambrian Stage 2 anoxic event. The outer shelf area experienced anoxia from Stage 2 to Stage 3 of the early Cambrian, although of possibly limited areal extent. The high Mobulk concentrations and Mo/TOCbulk ratios suggest that the South China basin was well connected with the considerably oxygenated open ocean and that the mean low δ15Nbulk values (∼+1.6‰) from the basin may reflect generally lower δ15N composition for seawater nitrate in the early Cambrian compared with modern value.