Journal of Paleontology, 92(2), 2018, p. 115–129 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.94


Diversity of cnidarians and cycloneuralians in the Fortunian (early Cambrian) Kuanchuanpu Formation at Zhangjiagou, South China


Tiequan Shao,1 Hanhua Tang,1 Yunhuan Liu,1* Dieter Waloszek,2 Andreas Maas,3 and Huaqiao Zhang4*


1School of Earth Science and Resources, Chang’an University, Xi’an 710054, China ⟨zytqshao@chd.edu.cn⟩, ⟨757230401@qq.com⟩, ⟨stotto@163.com⟩ 2University of Lund, Sölvegatan 12, SE-22362 Lund, Sweden ⟨dieter.waloszek@geol.lu.se⟩ 3Galgenackerweg 25, 89134 Blaustein, Germany ⟨maas.blaustein@freenet.de⟩ 4State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China ⟨hqzhang@nigpas.ac.cn⟩


Abstract.—The latest discovery of microfossils from the lower Cambrian (Fortunian Stage) Zhangjiagou Lagerstätte in South China are presented. This lagerstätte is rich in exceptionally preserved microfossils, including embryos of Olivooides multisulcatus, Olivooides mirabilis, and Pseudooides prima; hatched stages of O. multisulcatus, O. mirabilis, Hexaconularia sichuanensis,and Quadrapyrgites quadratacris; and cycloneuralians represented by Eopriapulites sphinx. The largest known fragment of O. mirabilis implies that its adult length can be more than 9.0mm with at least 50 annuli, and the longest known specimen of Q. quadratacris has at least 18 annuli. These unusually large specimens refute the non-feeding larvae hypothesis for Olivooides and Quadrapyrgites. Based on the current material, it is inferred that (1) early cnidarians have a high diversity in the Fortunian Stage;


(2) P. prima might represent the embryonic stages of H. sichuanensis; (3) adults of Olivooides and Quadrapyrgites may have reached centimeter-scale dimensions with more than 50 annuli; (4) Olivooides and Quadrapyrgites may be better interpreted as coronate scyphozoans; (5) cycloneuralians also had a high diversity in the Zhangjiagou Lagerstätte; and (6) cycloneuralians might have originally been part of the early Cambrian meiofauna rather than belonging to the macrobenthos. Such ancestral cycloneuralians might have been Eopriapulites-like, possessing pentaradially symmetric, backward pointing, and internally hollow introvert scalids used as locomotory devices.


Introduction


Molecular studies have suggested the first appearance of eumetazoans in the Ediacaran Period or earlier (Peterson et al., 2008; Erwin et al., 2011). However, this is not supported by fossil evidence because undisputed animal fossils in Precambrian rocks are extremely rare. The nature of fossil embryos from the Ediacaran Doushantuo Formation of South China (Xiao et al., 1998) is vague and has remained hotly debated (Xue et al., 1999; Bailey et al., 2007; Huldtgren et al., 2011; Chen et al., 2014). The material assigned to the earliest bilaterian animal Vernanimalcula guizhouena Chen et al., 2004 represents, most likely, artifacts of diagenesis (Bengtson et al., 2012). On the other hand, the fossil evidence demonstrates that all major groups of animals are already present early in the Cambrian Period (Budd, 2003a, 2013; Chen et al., 2007; Erwin et al., 2011; Erwin and Valentine, 2013; Budd and Jackson, 2015). This indicates that the early evolution of ani- mals took place well within the end of the Precambrian (Zhu et al., 2017). Cambrian strata preserve the earliest unambiguous animals and are thus crucial for uncovering not only the origin but also


* Corresponding authors


the major early steps and significant developments in metazoan evolution. The Fortunian Stage, the oldest stage of the Cambrian Period (Peng et al., 2012), is well known for the occurrence of skeletal remains known as small shelly fossils (SSFs). SSFs have a worldwide distribution, such as in Siberia (Voronova and Missarzhevsky, 1969; Val’kov, 1983), Australia (Bengtson et al., 1990), and South China (Qian and Bengtson, 1989; Steiner et al., 2004a), and they form the foundation of a global biostratigraphic correlation (Steiner et al., 2004a, 2007). Another important group of exceptionally preserved micro- fossils include taxa such as Olivooides Qian, 1977 (Bengtson and Yue, 1997; Donoghue et al., 2006a; Dong et al., 2016), Quadrapyrgites Li et al., 2007 (Liu et al., 2014a; Steiner et al., 2014), Pseudooides Qian, 1977 (Steiner et al., 2004b), a sea anemone (Han et al., 2010), the oldest known scalidophoran animals (Liu et al., 2014b; Zhang et al., 2015; Shao et al., 2016), the oldest known eumetazoan larvae (Zhang and Dong, 2015), and a plausible deuterostomian animal (Han et al., 2017). These exceptionally preserved microfossils have stimulated divergent interpretations and exciting debate on the origin and early evo- lution of animals. In the early Cambrian, the present-day southern Shaanxi


and northern Sichuan Provinces were located at the northern edge of the Yangtze Platform (Steiner et al., 2004a). On the


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