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

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.