Morphology and phylogeny of Bothriolepis yunnanensis (Placodermi, Antiarcha) from the Middle Devonian of China

Bothriolepis yunnanensis Liu, 1962, was first described based on an anterior median dorsal plate (assigned here as the lectotype) and a posterior median dorsal plate (assigned here as the paralectotype) from the Shangshuanghe Formation (Eifelian, Middle Devonian) in Qujing, Yunnan, southwestern China. Since then, no additional material has been assigned to B. yunnanensis, resulting in its morphology and phylogeny being poorly understood. In this study, we provide a comprehensive description of the head shield, trunk armor, and pectoral appendage of B. yunnanensis based on newly collected specimens from the type locality and neighboring sites in the Zhujiangyuan (Pearl River Source) area, Qujing. With the new fossil horizon in the Xichong Formation (Givetian), our latest findings extend the temporal range of B. yunnanensis to the entire Middle Devonian. Phylogenetic analysis shows that B. yunnanensis, B. zhujiangyuanensis, B. sinensis, and B. kwangtungensis from China and some Bothriolepis species from Laurussia and Kazakhstania are united into a clade sharing a slender proximal segment of the pectoral appendage, the absence of the median occipital crista, and a long posterior pit line. This result further corroborates the paleogeographic proximity between the South China and Kazakhstania blocks.