Distribution of the Silurian brachiopod genusAtrypoidea, and its first report in the Chejiaba Formation (upper Ludlow), Guangyuan, South China

Abstract

AbstractAtrypoideais a Silurian smooth atrypide with a worldwide distribution and high species-level diversity especially during Ludlow to Prídolí. In this study, the occurrences of 67 species, 14 subspecies, and 23 forma, cf., aff., or var. species are summarized. Among them,Atrypoidea rectafrom Aeronian of Siberia is the earliest known occurrence of this genus, whileAtrypoidea elatiororAtrypoidea polaris modicafrom upper Prídolí strata of the Czech Republic and China, respectively, should be the youngest species. No valid Devonian occurrence ofAtrypoideahas been recorded due to absence of convincing identification or poor stratigraphic information. The rapid evolution and cosmopolitan nature ofAtrypoideaallow some species to be used as index fossils for strata of Ludlow and Prídolí in South China. The age of the Chejiaba Formation in Guangyuan, Sichuan Province, South China, has been clarified based on the occurrence ofAtrypoidea. Specimens from this locality, which are preservedin situ, are described herein and illustrated with reconstruction of life style for the first time.