Journal of Paleontology, 92(6), 2018, p. 1081–1091 Copyright © 2018, The Paleontological Society 0022-3360/15/0088-0906 doi: 10.1017/jpa.2018.18


The enigmatic metazoan Yuyuanozoon magnificissimi from the early Cambrian Chengjiang Biota, Yunnan Province, South China


Yujing Li,1,2,3 Mark Williams,2,3 Sarah E. Gabbott,2,3* Ailin Chen,1,3,4 Peiyun Cong,1,3,5 and Xianguang Hou1,3*


1Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091, China ⟨yl@mail.ynu.edu.cn⟩, ⟨cong@ynu.edu.cn⟩, ⟨xghou@ynu.edu.cn⟩ 2School of Geography, Geology and the Environment, University of Leicester, Leicester LE1 7RH, UK ⟨mri@leicester.ac.uk⟩, ⟨sg21@leicester.ac.uk⟩ 3MEC International Joint Laboratory for Palaeobiology & Palaeoenvironment, Yunnan University, Kunming 650091, China 4Research Center of Paleobiology, Yuxi Normal University, Yuxi 653100, China ⟨ailinchen@yxnu.net⟩ 5Department of Earth Sciences, The Natural History Museum, London SW7 5BD, UK


Abstract.—Vetulicolians are a group of exclusively Cambrian animals characterized by an anterior section with lateral pouches and a posterior section that appears segmented. The precise phylogenetic affinity of vetulicolians is debated because there is a lack of consensus regarding the interpretation of their anatomical features. Their disparate morphology might even cause one to question whether this is a monophyletic taxon. In total, there are 15 species grouped into three families included in vetulicolians. Here we focus on new specimens of Yuyuanozoon magnificissimi Chen, Feng, and Zhu in Chen et al., 2003, a species that was first described from only a single specimen from the Chengjiang Biota (Cambrian Series 2, Stage 3, Eoredlichia-Wutingaspis trilobite Biozone), Yunnan Province, China. The species is notable in being exceptionally large (up to 20 cm long). Morphological observations on the new specimens clarify the nature of the wide circular opening at the presumed anterior end of the animal and the cowl-shaped lateral openings within this anterior sec- tion. Taphonomic observations identify wrinkles in the anterior section and twists in the posterior segmented section. In particular, the shape of the anterior opening of Yuyuanozoon magnificissimi suggests significant differences from other vetulicolians. Taxonomic reappraisal of Y. magnificissimi indicates that it belongs within the family Didazoonidae, as that is presently defined.


Introduction


As currently understood, vetulicolians are a group of exclusively marine, enigmatic, and extinct Cambrian animals represented by three families: the Vetulicolidae, the Didazoo- nidae, and the Banffidae (Aldridge et al., 2007). They are characterized by a bipartite body. The anterior part is covered by a structure that superficially resembles the carapace of many arthropods. This structure, here referred to as the anterior section (Fig. 1), contains five lateral pouches, some possessing a lateral groove on each side, that have been interpreted by some as possible gill slits (Shu et al., 2001). The posterior section resembles the arthropod trunk, possessing a segmented and sometimes annulated morphology. Soft-part anatomy has been reported in some vetulicolians, including structures interpreted to represent muscle fibers (Aldridge et al., 2007; Ou et al., 2012; García-Bellido et al., 2014). The vetulicolian body plan and the limited information about soft-bodied anatomical structures within the anterior section make the interpretation of these animals difficult. As a result, the phylogenetic position of vetulicolians is unclear, with proposed affinities much debated and varying from their interpretation as unusual arthropods (Hou, 1987; Caron, 2006), kinorhynchs (Aldridge et al., 2007),


* Corresponding authors


or stem-group deuterostomes (Shu et al., 2001; Ou et al., 2012) or chordates (Lacalli, 2002; García-Bellido et al., 2014). Vetulicolians, as currently understood, are represented by


15 species, which occur worldwide but only in Cambrian Lagerstätten, including the Chengjiang Biota (Hou, 1987; Luo et al., 1999; Shu et al., 2001; Chen et al., 2003; Shu, 2005; Aldridge et al., 2007), the Guanshan Biota (Luo et al., 2005; Yang et al., 2010; Li et al., 2015), and the Shipai Formation of South China (Zhang and Hua, 2005); the Burgess Shale (Wal-


cott, 1911) and the Mural Formation, both in Canada (Butter- field, 2005); the Sirius Passet Biota of Greenland (Vinther et al., 2011); the Emu Bay Shale of Australia (García-Bellido et al., 2014); and the Spence Shale in Utah, USA (Briggs et al., 2005; Conway Morris et al., 2015). They are known almost exclu- sively from their characteristic anterior section, which possesses lateral pouches, and segmented posterior section. Despite being widespread and common animals throughout Cambrian Lager- stätten, the affinity of vetulicolians remains controversial. Yuyuanozoon magnificissimi Chen, Feng, and Zhu in Chen


et al., 2003 is exceptionally large, being up to 20 cm in length, compared with other vetulicolian species, which are generally 5–14 cm long. Thus far, it has been described from a single complete specimen, but here we show by reference to new material that some of the characteristics of this original speci- men have been modified postmortem, and as such its current


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