Article

New Sponges from the Lower Cambrian of Guizhou

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... South China represents a unique region for the study of early-life evolution due to its well-developed Cambrian stratal successions, high-resolution chronostratigraphy and rich fossil records (Luo et al., 1994;Zhu et al., 2007;Zhang et al., 2008;Ishikawa et al., 2008Ishikawa et al., , 2013Ishikawa et al., , 2014Peng, 2009). Many well-preserved fauna were recovered from Series 2 in South China, including the Qingjiang Biota (Fu et al., 2019), Chengjiang Biota (Zhang and Hou, 1985;Hou et al., 1999;Shu et al., 2014), Guanshan Biota (Luo et al., 1999), Zunyi Biota (Yang et al, 2005;Zhao et al., 1999;Steiner et al., 2005), Malone Biota (Luo, 1992;Luo et al., 2008), Balang Biota (Sun et al., 2015;Peng et al., 2016), Shipai Biota (Zhang and Hua, 2005;Zhang et al, 2008), Niutitang Sponge Fauna (Zhao et al., 1999;Steiner et al., 2005), Hetang Sponge Fauna (Xiao et al., 2005) and others. These discoveries provided strong evidence for the Cambrian Explosion and diversification events in metazoans evolution history both in shallow-water environments (e.g., shallow shelf-Chengjiang Biota, Guanshan Fauna; platform margin-Zunyi Biota, Malone Biota, Balang Biota) and deep-water environments (e.g., upper slope settings-Niutitang Sponge Fauna, Qingjiang Biota; lower slope settings-Hetang Sponge Fauna). ...
Article
Abundant metazoans phyla made their first appearances in the fossil record during a relatively short time span in the Ediacaran-Cambrian interval (560–520 Ma) and rapidly expanded ecologically during the early Cambrian, leading to the establishment of metazoan-dominated ecosystems accompanied by widespread biomineralization. This unique evolutionary event was known as the ‘Cambrian Explosion’. Although a significant amount of work has been undertaken to understand the evolution of life during this time interval, previous studies have mainly focused on fossil records from the Cambrian fine-grained clastic rocks deposited in shallow-water environments. However, fossil records from marlstones and mudstones formed in deep-water basins were poorly understood. In this study, we focus on fossil records from the black thin-bedded marl and calcareous mudstones of the lower Cambrian Shuijingtuo Formation in the Three Gorges area, Hubei Province. A total of 9059 fossil specimens, including both microfossils and megafossils belonging to 45 species and 14 major taxonomic groups were recovered from the Shuijingtuo Formation at the Luojiacun section. Four palaeoecological assemblages were recognized based on fossil composition and ecological characteristics. The oldest assemblage (Assemblage A) features an Isoxys-dominated planktonic community with only one benthic group of bradoriids and exhibits the highest fossil abundance and lowest species diversity. Assemblage B is characterized primarily by highly diverse benthic groups, which in decreasing order of abundance include bradoriids (27.4%), sponge spicules (9.8%), cnidarians (5.7%) and hyoliths (2.0%). The third assemblage (Assemblage C) introduces the predominant role of sponge spicules, which compose 44.8% of the community. In contrast, Assemblage D is predominated by phytoplankton featuring the lowest fossil abundance and low diversity. Integration with geochemical and sedimentary data indicates that these biotic assemblages and their evolution were mainly controlled by environmental redox variations and changes in terrestrial fluxes and water depth, subsequently suggesting a significant role of these factors on biotic evolution in the early Cambrian deep-water environment. This study provides support for the importance of oxygen levels in the evolution of life during the early Cambrian.
... Taxonomic data were taken from previous publications (Cong et al., 2018Du et al., 2018;Fu et al., 2019;Guo et al., 2019;Han et al., 2019;Hou et al., 2017;Ou and Mayer, 2018;Shu et al., 2017;Steiner et al., 1993;Sun et al., 2018a;Tang et al., 2019;Wu et al., 2014Wu et al., , 2005Xiao et al., 2005;Yang et al., 2016Yang et al., , 2015Yang et al., 2005aYang et al., , 2005bYang et al., , 2010Yun et al., 2017;Zeng et al., 2017Zeng et al., , 2014Zhao et al., 2017Zhao et al., , 2014Zhao et al., , 2012 supplemented by data obtained from the new fossil material reported here (Tables S1, S2). To minimize bias, fossil identifications were limited to the level of genus. ...
... There are abundant sponges in articulate preservation from the lower Cambrian black shale of South China, including the Niutitang sponge fauna in Guizhou (Yang, 2002;Yang et al., 2005aYang et al., ,b, 2010 and Hunan (Steiner et al., 1993;Mehl and Erdtmann, 1994), Hetang and Huangbeiling sponge faunas in southern Anhui (Wu et al., 2005;Xiao et al., 2005). Like the Chengjiang sponge fauna, the Niutitang sponge fauna (A) at Zhongnan, Songlin in northern Guizhou is found in the Niutitang Formation from the shallow water facies; it consists of 13 genera, 55% of which are demosponges (see Table 1). ...
Article
Sponges are dominant sessile suspension feeders in the Cambrian metazoan community; thus, sponge tiering and composition in the Cambrian communitieswill provide important information for elucidating the evolutionary history of the epifaunal community. Based on more than two thousand articulated sponge specimens from the early Cambrian Chengjiang fauna, the present study demonstrates that the Chengjiang sponge community is dominated by demosponges with a well-developed three-level tiering, consisting of 0–5 cm, 5–15 cm and 15–30 cm tiers. The majority of the sponges are restricted to the 0–15 cm tier, suggesting rich nutrients in the bottom seawater of the Cambrian ocean. Tiering in the Cambrian sponge communities is consistent and similar to that of the Ediacaran and Phanerozoic epifaunal communities, but the fourth tier (50–100 cm) in these latter communities is absent in the Cambrian communities. Demosponges dominate the shallow-water sponge communities and occur in all tiers. Hexactinellids are relatively rare and limited in the lower tiers in the shallow water community, but dominate in the deep-water communities. The composition variation in the Cambrian sponge communities may be controlled by the differences in skeleton architecture between the Demospongiae and Hexactinellida.
Article
The Cambrian strata in southern Hunan can be divided from bottom to top into Xiangnan Formation, Chayuantou Formation and Xiaozijing Formation. The rock types are mainly clastic rock and subordinately carbonate rock and siliceous rock, in which sandstone and mudstone (shale)often form typical flysch rhythms. Based on a comprehensive study of such facies indicators such as lithologic character, palaeobiologic fossils and sedimentary structure, the authors hold that the Cambrian sedimentary environment of the study area was a deep-water slope to basin environment. The sedimentary environment evolution was analyzed and the sedimentary model was set up. The area experienced three transgression events during Cambrian. The first transgression began in the Jinning stage and ended in the Nangao stage. The second transgression began in the Duyun stage and ended in the Wangcun stage. The third transgression began in the Guzhang stage and lasted until the Niuchehe Age.
Article
The Cambrian strata are widely distributed in western Hubei area. Abundant Sunella (Bradoriida), Perspicaris (large bivalved arthropods), macroscopic algal, hyolithes and (?)Sinospongia (Suspicious sponges) have been found in the lower black carbonaceous shale of the Cambrian Niutitang Formation from Tianzhu area of Changyang County, Hubei Province. In addition, scattered pyrite is seen in black shale. Based on a detailed study of palaeoecology and the characteristics of fossils preservation, the authors have reached the conclusion that, during the early sedimentary stage of Niutitang Formation in Changyang County of western Hubei Province, macroorganism lived in an environment of shallow water which was suboxic at the bottom, oxic in the upper part characterized by good light transmission and relative calmness, and that the sea bottom surface was located nearby the redox interface. Besides, under the background of rapid deposition, large amounts of water and dead biological-bodies were embedded in shale, the amount of water exchange between the depositional water and the external water decreased gradually, and H 2S gas was generated by rotton organism in the process of deposition, forming a strong reduction environment in sediments, so that organic matter could be preserved, which eventually formed black shale.
Article
Sponges are among the earliest diverging crown-group animals and widely regarded as the earliest biomineralizing animals. Indeed, unambiguous hexactine sponge spicules first occur in the lowermost Cambrian strata of the Fortunian Stage. Articulated sponge skeletons interpreted as hexactinellids and demosponges have been reported from Cambrian Stage 2-3 strata at multiple localities. Articulated sponge skeletons in the Chengjiang biota (Cambrian Stage 3), however, are dominated by forms interpreted as demosponges, despite the exceptional preservation in this biota. Here, we report new articulated sponge skeletons from the Chengjiang biota, including Paradiagoniella magna n. gen. n. sp. and P. xiaolantianensis n. gen. n. sp. The skeleton of both species consists of ranked stauractines and rare oxeas (straight or curved diactines), as well as hexactines in the former species. Their stauractines form irregular, nested, local sub-quadrules oriented obliquely to the sponge body axis. Sub-quadrules of different ranks are not in parallel arrangement. The two species are tentatively placed in the family Protospongiidae, which as currently defined may be a paraphyletic group including members of the total-group hexactinellids and perhaps stem-group siliceans. The phylogenetic placement of P. magna and P. xiaolantianensis is uncertain but, like many other protospongiids, they could be members of the total-group hexactinellids or stem-group siliceans. The diactines in the two species could be secondarily reduced hexactine-based spicules; alternatively, these two species may represent an evolutionary grade of stem-group siliceans with both diactines and hexactine-based spicules, the latter of which was lost in demosponges. A comprehensive cladistics analysis is needed to resolve the exact phylogenetic placement of the two species described here.
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