Darriwilian graptolites of the Shihtien Formation (Ordovician) in west Yunnan, China

West Yunnan in southwestern China formed an important part of the Sibumasu Terrane during the Ordovician. The Ordovician rocks of the region are exposed at many localities but have been strongly affected by several phases of tectonic activity, especially by the most recent Himalayan phase that commenced in the Paleogene. For these reasons, together with the difficult access to the localities, the Ordovician graptolites and biostratigraphy of this region are rather poorly known. Herein, we describe a Darriwilian graptolite fauna from the Shihtien Formation at Baoshan and Shidian, western Yunnan. The fauna comprises 11 genera and 15 species, including Didymograptus artus, D. murchisoni, D. spinulosus, Pterograptus sp., Hustedograptus vikarbyensis, H. teretiusculus, Archiclimacograptus angulatus, A. riddellensis, Haddingograptus oliveri, Proclimacograptus angustatus, and the dendroids Dictyonema, Palaeodictyota, Dendrograptus, Callograptus and Ptilograptus, indicating an age of middle to late Darriwilian. Two graptolite biozones are recognized: the Didymograptus artus and Didymograptus murchisoni biozones, in ascending order. The graptolite fauna is substantially similar to those of Baltica and South China.