1082
Journal of Paleontology
Figure 1. A hypothetical vetulicolian, showing detailed morphological characters. Abbreviations are as follows (terms used by other authors are in parentheses). Ac=alimentary canal (gut); An=anus; Ao=anterior opening (oral opening, oral, mouth, head); Ar=articulation; As=anterior section (anterior body, carapace, head +trunk), presumed cover of the anterior part of the body; Dp=posterodorsal projection (fin-like structure, dorsal fin, fin); Ds=dorsal section; Fs=filamentous structures (gill filaments); Lg=lateral groove, a lateral midline that consists of a longitudinal groove associated with five openings at each side of the anterior section; Lp=lateral pouches/openings (gill pouches, serial lateral opening structure); Ls=lateral slit (gill slit); M=membrane; Ps=posterior section (posterior body, tail, abdomen), posterior part of the body; S=segment; S1–S7=first through seventh segment of posterior section; Vp=posteroventral projection of anterior section (fin-like structure, ventral fin); Vs=ventral section.
appearance does not accurately represent in vivo morphology. Here we describe new specimens, provide a new interpretation for the opening at the presumed anterior end of the animal, and reassign this taxon to the vetulicolian family Didazoonidae.
Geologic setting
The early Cambrian Chengjiang Lagerstätte (Cambrian Series 2, Stage 3, Eoredlichia-Wutingaspis trilobite Biozone of Eastern Yunnan, a biostratigraphical interval equivalent to part of the Ush- baspis trilobite Zone of South China) occurs through a 30–50 m thick succession of claystones that have been celebrated for yielding about 250 species of soft-bodied and weakly biomineralized organisms (Hou et al., 2017). The dominant component of the biota, both in numerical abundance and species diversity, is arthropods, but lobopodians, sponges, brachiopods, some enigmatic animals and chordates are also represented (Hou et al., 2017). Other sig- nificant animals are the vetulicolians, of which the Chengjiang Biota contains the greatest diversity and numbers from the Cam- brian System worldwide. The three new specimens of the vetulicolian Yuyuanozoon
magnificissimi described here are from the Ercaicun section at Haikou, Kunming area, Yunnan Province, about 30 km south of Kunming city and about 50km northwest of Maotianshan, the original locality from which Chengjiang fossils were discovered (see Hou et al., 2017 for the history of the Chengjiang Biota).
Materials and methods
The specimens were prepared using steel needles and examined with a Nikon SMZ–10A binocular microscope. We used a
camera lucida attached to aWild Heerbrug M10 microscope to elucidate and record the anatomy. The digital images of the specimens were captured with Nikon D3X and Canon 500D digital cameras and a Leica DFC5000 camera attached to a Leica M205C photomicroscope and were processed in Adobe Photoshop CC. All measurements were processed with ImageJ version 1.49.
Repository and institutional abbreviation.—The three new specimens documented here are preserved with part and coun- terpart and are deposited in the Yunnan Key Laboratory for Palaeobiology, Yunnan University (abbreviated YKLP), Kunming, China, with numbers YKLP 13070, YKLP 13071, and YKLP 13072.
Morphology and terminology of the vetulicolian body
The anatomical terms applied to vetulicolians are complicated because there is no consensus on a common nomenclature in different publications. Vetulicolian taxonomy sometimes uses a range of standard morphological terms such as ‘carapace’ and ‘gill slits’ (see Table 1), though there is no certainty of the homology of such structures between taxa, or even whether these terms, some for example borrowed from arthropod terminology (e.g., for the genus Skeemella), are appropriate. Here we use descriptive terms carefully, to avoid inference
about evolutionary significance, thus avoiding the potential for circular reasoning regarding phylogenetic interpretation. For example, we do not use the term ‘carapace’ to denote the anterior section of the animal. Our morphological terms are
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