Nostolepis scale remains (stem Chondrichthyes) from the Lower Devonian of Qujing, Yunnan, China

Based initially on microfossils, Nostolepis is one of the first known 'acanthodians', which constitute a paraphyletic assemblage of plesiomorphic members of the total group Chondrichthyes. Its wide distribution has potential implications for stratigraphic comparisons worldwide. Six species of Nostolepis have been reported in China, including one species from the Xitun Formation (Lochkovian, Lower Devonian) of Qujing, eastern Yunnan. Acid preparation of rock samples from the Xitun Formation has yielded abundant acanthodian remains. Based on both morphological and histological examinations, here we identify five species of Nostolepis, including two new species. N. qujingensis sp. nov. is characterized by thin scales devoid of the neck anteriorly and the dentine tubules rarely present in the anterior part of the crown. N. digitus sp. nov. is characterized by parallel ridges on anterior and lateral margins of the crown, and the neck constricted and ornamented with pore openings. We extend the duration of N. striata in China from the Pridoli of Silurian (Yulungssu Formation) to the Lower Devonian in Qujing and report the first occurrences of N. amplifica and N. consueta in this region. This study increases the diversity of the Lower Devonian Xitun Fauna and provides a better understanding of the paleogeographic distribution of Nostolepis.