Discovery of the late Middle Ordovician Saucrorthis fauna (Brachiopoda) from the Sibumasu palaeoplate, western Yunnan, SW China

Abstract

A relatively diverse Saucrorthis brachiopod fauna is reported for the first time from the Sibumasu palaeoplate in the Shihtien Formation (Darriwilian, upper Middle Ordovician) at Laojianshan of Baoshan, western Yunnan Province, southwest China. It contains 25 brachiopod genera, amongst which orthides, strophomenides and billingsellides are predominant, but quantitatively Saucrorthis and Leptestiina are the most abundant. Numerical analyses of 23 global Darriwilian brachiopod faunas show two major clusters, the Saucrorthis Group and the Aporthophyla Group, representating two major palaeobiogeographical regions developed during the Darriwilian, corresponding to lower and higher palaeolatitudinal habitats, respectively.

Keywords::

• Saucrorthis fauna
• Darriwilian (Middle Ordovician)
• Baoshan of Yunnan
• Sibumasu palaeoplate

Acknowledgements

Fan Junxuan, Ma Xuan, Wang Yuan and Guo Zhengfu from the Nanjing Institute of Geology and Palaeontology (NIGP) extended their help in the field. Critical reviews by Ian Percival and Christian Rasmussen, and suggestions from journal editors, Mikael Calner and David Harper, greatly helped improve the presentation of this manuscript. Financial supports are from the Chinese Academy of Sciences (CAS), the National Nature Science Foundation of China (40825006, 41221001, 41290260) and the State Key Laboratory of Palaeobiology and Stratigraphy (LPS). This paper is a contribution to the IGCP project 591 “The Early-Middle Paleozoic Revolution”.