Journal of Paleontology, 92(1), 2018, p. 49–58 Copyright © 2017, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.50


New paleoscolecid worms from the early Cambrian north margin of the Yangtze Platform, South China


Yuning Yang,1,2 Xingliang Zhang,3 Yuanlong Zhao,1 Yiru Qi,3 and Linhao Cui3


1College of Resource and Environment Engineering, Guizhou University, Guiyang 550025, China ⟨ynyang333@163.com⟩, ⟨zhaoyuanlong@126.com⟩ 2State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences),


Nanjing 210008, China 3State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China ⟨xzhang69@nwu.edu.cn⟩, ⟨qiyiru1988@163.com⟩, ⟨570325901@qq.com⟩


Abstract.—The Cambrian Yanwangbian assemblage (Series 2, Stage 4) in South Shaanxi, China, is one of the Burgess Shale–type faunas as it represents the only relatively diverse Cambrian biota from the north margin of the Yangzte Platform, South China. The paleoscolecids (Cycloneuralia) illustrated herein are one of the major compo- nents of the fauna, although they appear to be much less abundant than skeletonized fossils, according to available collections. A new taxon, Shaanxiscolex xixiangensis new genus new species, is described based on the scleritome pattern: each annulus has two rows of alternating Hadimopanella-type plates positioned close to the borders, and a mosaic pattern of microplates occurs between the plates and within intersegmental furrows. The occurrence of the new taxon confirms a fairly diversified and widespread distribution of paleoscolecidan worms recognized in the early Cambrian of South China. Moreover, the ecology of paleoscolecids is reappraised based on burial position of the S. xixiangensis and gut contens of Cambrian taxa from South China, hinting that paleoscolecids (at least some taxa) were both deposit feeders and carnivores, as well as active bioturbators in the substrates of the Cambrian sea, which sheds new light on the ‘Cambrian Substrate Revolution.’


Introduction


The fossil records of paleoscolecidan worms, a group that is characterized by slender, multiannulated bodies covered with distinctive armor of minute phosphatic sclerites and known from Cambrian to Silurian, are better than for any other Cycloneuralia (Maas, 2013). Because of their macroscopic, introvert-bearing, and broadly priapulid-like body plan, the extinct paleoscolecids are assumed to have allowed for the expectations of symplesiomorphies of ancestral ecdysozoans (Budd and Jensen, 2000; Budd, 2001, 2008; Zrzavý, 2003; Webster et al., 2006), which make these animals a vital component for understanding early evolution of stem group Cycloneuralia within ecdysozoans. Many researchers, however, have suggested that paleoscolecids shared classical morphology and developmental biology with stem priapulids (Conway Morris, 1997; Huang, 2005; Han et al., 2007b; Hu et al., 2012; Wills et al., 2012), but not with panarthropods (Harvey et al., 2010), although a more robust analysis of their affinities is required for assessing the significance for ecdysozoan evolution. Furthermore, since incomplete diagnoses and unde- tected synonymies are common in this group, considerable problems arise in many cases when comparisons are made among morphological characters of fossils preserved in different styles and of variable quality (Conway Morris and Peel, 2010;


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Harvey et al., 2010; Topper et al., 2010; García-Bellido et al., 2013; Yang and Zhang, 2016). The fossil records of compressed paleoscolecids preserving


an armored terminal introvert from several Cambrian deposits (e.g., Hou and Bergström, 1994; Chen, 2004; Hou et al., 2004; Huang, 2005; Han et al., 2007b; Maas et al., 2007; Dornbos and Chen, 2008; Conway Morris and Peel, 2010; Hu et al., 2012; García-Bellido et al., 2013; Yang and Zhang, 2016) provide opportunities to constrain their taxonomies and precise affi- nities. Except for the frontal introvert, however, cuticle orna- mentation (e.g., plates, platelets, and microplates) in compression paleoscolecids, which are the key characteristics in taxonomic purposes of the group (Conway Morris, 1997; Botting et al., 2012), are unfortunately poorly preserved. In addition, most of these macrofossil taxa from South China are generally confined to shallow water and epeiric sea platform facies around the center of the Yangtze Platform (Yang, 2016). In this paper, a macroscopic paleoscolecid, Shaanxiscolex


xixiangensis new genus new species, is reported from the Cambrian Yanwangbian Formation in the north margin of the Yangtze Platform mainly on the basis of its well-preserved scleritome pattern. In addition, a set of S. xixiangensis buried in life position along with some other Cambrian paleoscolecids from South China, provide valuable information in analyzing the ecology of this extinct class. Accordingly, the occurrence of


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