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

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 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, a species that was first described in 2003 based on a single specimen from the Chengjiang Biota (Cambrian Series 2, Stage 3, Eoredlichia-Wutingaspis trilobite Biozone), Yunnan Province, China. Although placed in the family Vetulicolidae, this 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 ovoid shape of lateral openings within this anterior section. 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 re-appraisal of Y. magnificissimi indicates that it likely belongs within the family Didazoonidae, as that is presently defined.

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