Journal of Paleontology, 92(6), 2018, p. 955–971 Copyright © 2018, The Paleontological Society 0022-3360/15/0088-0906 doi: 10.1017/jpa.2018.43


New well-preserved scleritomes of Chancelloriida from early Cambrian Guanshan Biota, eastern Yunnan, China


Jun Zhao,1,2 Guo-Biao Li,1,2* and Paul A. Selden3,4


1State Key Laboratory of Environmental Geology and Biogeology, China University of Geosciences, Beijing, 100083, China ⟨zhaojunpaleo@126.com⟩, ⟨liguobiao@cugb.edu.cn⟩ 2School of Earth Sciences and Resources, China University of Geosciences, Beijing, 100083, China 3Department of Geology, University of Kansas, 1457 Jayhawk Boulevard, Lawrence, KS 66045, USA ⟨selden@ku.edu⟩ 4Natural History Museum, Cromwell Road, London SW7 5BD, UK


Abstract.—A large number of well-preserved chancelloriid scleritomes from the Guanshan biota, early Cambrian of Yunnan, China, are described as a new species, Allonnia tenuis n. sp., and provide solid evidence for the original appearance of these enigmatic animals, based on specimens compacted laterally and top-down. With the assistance of a flexible integument, chancelloriids, especially Allonnia from early and middle Cambrian, may have had the ability to partially or completely expand and contract the body, which might have played an important role in feeding. A new metazoan with single-element spines, Nidelric gaoloufangensis n. sp., is also described. Preservation and affinity are discussed. Detailed comparison of the morphology of the body and spines of this metazoan indicate that it shares many similarities with chancelloriids, of which it may be an unusual form.


UUID: http://zoobank.org/2708d95a-1fae-46fc-afea-9707ae97a4d7


Introduction


Chancelloriids are a group of organisms of problematic affinity, which are characterized by a sac-like body covered with spiny sclerites. Complete specimens (scleritomes) show them to be sessile, cylindrically symmetrical metazoans, having a general morphology reminiscent of that of a barrel cactus (Bengtson and Hou, 2001; Janussen et al., 2002; Randell et al., 2005; Moore et al., 2014). They are found stratigraphically from the Terre- neuvian to the Furongian in the Cambrian (Bengtson and Hou, 2001; Janussen et al., 2002; Hong et al., 2016). Well-preserved chancelloriid scleritomes from the early and middle Cambrian occur mainly in China, Canada, and the USA (Bengtson and Collins, 2015). The late Cambrian witnessed a rapid decline of chancelloriids and only a few occurrences have been described (e.g., Mostler and Mosleh-Yazdi, 1976). By the end of the Cambrian, this problematic group had probably become extinct (Janussen et al., 2002). The phylogenetic position of chancelloriids remains


skeleton typical of sponges. Chancelloriids, along with halkieriids, siphogonuchitids, and sachitids, were placed by Bengtson and Missarzhevsky (1981) in the Coeloscleritophora. This proposal was followed by some researchers (e.g., Qian and Bengtson, 1989; Bengtson et al., 1990; Bengtson, 2005; Porter, 2008;Moore et al., 2010), but again rejected by others because of the differences in anatomy between chancelloriids and the halkieriids: the former are cylindrically symmetrical whereas the latter are bilaterally sym- metrical (Conway Morris and Peel, 1995; Vinther and Nielsen, 2005). Subsequently, chancelloriids have been considered to be related to tunicates (Mehl, 1996), cnidarians (Randell et al., 2005), mollusks (Conway Morris and Peel, 1995; Vinther and Nielsen, 2005; Conway Morris and Caron, 2007; Vinther, 2009), or to lie elsewhere in the early branches of the Metazoa (Janussen et al., 2002; Sperling et al., 2007). After detailed studies, chancelloriids, with potential eumetazoan plesiomorphy (coelosclerites), were suggested likely to belong to a parayphyletic Coeloscleritophora (Bengtson and Collins, 2015). In recent years, more and more articulated scleritomes of


unsolved. They were first considered to be problematic fossils (Bornemann, 1886; Rosén, 1919). Walcott (1920) described chancelloriids as heteractinid sponges based on their sponge- like appearance and sclerite morphology. This taxonomy was accepted by a number of workers for more than half a century (e.g., Laubenfels, 1955; Sdzuy, 1969; Finks, 1970; Mostler, 1980, 1985), but rejected by Goryansky (1973), who argued that chancelloriids have an external skeleton, rather than the internal


* corresponding author


have been considered variously as predators, filter feeders, fee- ders of dissolved organic matter, and symbiotrophs (Chen et al., 1996; Bengtson and Hou, 2001; Janussen et al., 2002; Randell et al., 2005; Sperling et al., 2007; Kloss et al., 2009). The


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chancelloriids have been described in early and middle Cambrian faunas, which have definitely helped our understanding of the ori- ginal appearance of these problematic animals. Here, we describe a new species of chancelloriid and a newchancelloriid-likemetazoan. Both species occur in great numbers and are well preserved. The feeding mode of chancelloriids remains unclear; they

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