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Niutitang Biota at Zhongnan village, Songlin town, Zunyi County, northern Guizhou Province, China

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Early Cambrian (Tommotian) black shales in South China contain submarine-hydrothermal exhalative sulfide ore layers within an arc-parallel linear belt extending more than 1600 km. Evidence for an Early Cambrian hydrothermal venting is given by the records of main and trace elements, rare earth elements (REE), sulfur isotopes and the petrological and geological investigations. Mass occurrences of arthropods, sponges and undetermined shelly remains co-occur with hydrothermal vent deposits in the basal Niutitang Formation at the Sansha (Hunan Province) and Zunyi sections (Guizhou Province). This fauna, although not considered as vent fauna sensu stricto, appears linked to the hydrothermal vents via primary and secondary consumption on lithochemotrophic primary producers. Mats of sheathed sulfur bacteria are common in contemporaneous black shales nearby the vent localities. The ‘Cambrian explosion’, an event of probably rapid biological diversification, is discussed here in context of adaptation to shallow water habitats and major changes in trophic resources. According to our new hypothesis metazoans may have already existed in deep-sea hot vent areas during the Precambrian. This unique ecological niche also supplied favourable habitats for metazoans during the Neoproterozoic supposedly world-wide Varanger glaciation. Cessation of deep ventilation and expansion of dysoxic conditions into shelf areas may have driven the migration of metazoans from hydrothermal vents to shallow water areas in the earliest Cambrian thus enhancing both evolutionary opportunities and the chance of preservation in the geologic record.
Epifaunal, suspension-feeding bilaterian animals in the Cambrian lived close to the sediment-water interface, and hence their ecological tiering levels were low (<10 cm). Here we report an Early Cambrian (Diandongian or probably Tommotian-Atdabanian) Lagerstätte from the Hetang Formation in Anhui Province, south China. The Hetang biota is characterized by high-tiering (to 50 cm) sponges and small (<0.5 cm) bilaterians (including orthothecid hyoliths and bivalved arthropods). Nonbilaterian suspension feeders (sponges, cnidarians, and archaeocyathids) as high-tiering animals and bilaterian suspension feeders as low-tiering animals also characterize other Neoproterozoic-Cambrian assemblages, such as the Ediacaran, Chengjiang, Burgess Shale, and Sinsk biotas. These data are consistent with medium- to high-tiering levels in Neoproterozoic-Cambrian epifaunal communities, but suggest that nonbilaterians achieved such tiering levels long before bilaterian suspension feeders did so in the Early Ordovician. The disparity between bilaterian and nonbilaterian tierers during the Neoproterozoic-Cambrian transition and the delayed appearance of high-tiering bilaterians demand phylogenetic and ecological explanations. The Cambrian substrate revolution may have triggered a cascade of ecological evolution, including the rise of bilaterian animals in high-tiering levels during the Ordovician radiation of the Paleozoic fauna.
Burgess Shale-type preservation has been reported from numerous Qiongzhusian and Canglangpuian sections of southern China during the last few decades. The Early Cambrian Chengjiang-type faunas of East Yunnan were of particular interest due to their excellent preservation and taxonomic diversity. A new definition and revision of the Chengjiang-type faunas is given, which indicates that distinct ecological variations occurred between the Chengjiang and Haikou faunas on a smaller scale, and between the arthropod-dominated faunas of shallow shelf and the sponge-dominated faunas of deeper shelf (e.g. Hunan) on a larger scale. Recent finds from the Yuanshan Formation of Deze, East Yunnan, and the Niutitang Formation of Zhongnan, Zunyi County, Guizhou, indicate a much wider distribution of Burgess Shale-type fauna during this period than was previously known. The present investigations of the latter fauna revealed the presence of Tsunyidiscus niutitangensis, Naraoia spinosa, N. cf. longicaudata, Isoxys curvirostratus, I. paradoxus, Skioldia aldna, Amplectobelua trispinata, cf. Tsunyiella diandongensis, Scenella sp., Cambrorhytium elongatum, Hyalosinica archaica, and Choiaella radiata. The occurrence of Burgess Shale-type preservation on the Yangtze Platform is not restricted to a small area as in the Burgess Shale, but known from a ca. 80 km wide geographic stripe extending for more than 500 km along the rim of Proterozoic platform core. This wide distribution of Burgess Shale-type preservation is interpreted to be triggered by the coincidence of specific palaeoecological conditions, including the rapid sedimentation of finest siliciclastic particles and the partial influence of suboxic water masses.
Two species of Sphenothallus (Cnidaria) from Cambrian rocks of eastern Guizhou, China, are reported. One species, Sphenothallus songlinensis n. sp., from the Niutitang Biota (Lower Cambrian: Nangaoan Stage), represents the oldest reported example of the genus. Other specimens, referred to Sphenothallus taijiangensis?, are from the Kaili Formation (Lower Cambrian: Duyuanian Stage). The new material adds to the record of sessile cnidarians, an important group of predators, from the early part of the Cambrian. Occurrences of the genus in strata traditionally assigned to the Lower Cambrian show that Sphenothallus was among the earliest animals to produce a biomineralized (phosphatic) skeleton.