Middle and Upper Cambrian protoconodonts and paraconodonts from Hunan, South China

More than 4200 kg of limestone, representing 980 productive samples, from t he upper Middle Cambrian, Upper Cambrian, and lowermost Ordovician in weste rn and north-western Hunan were processed for paraconodonts, protoconodonts , and euconodonts. The focus of the present paper is on the upper Middle an d lower Upper Cambrian interval as it is developed at two, apparently strat igraphically continuous, key sections. The collections studied, which inclu de more than 20,000 specimens and are quite diverse taxonomically, prove th at some protoconodonts and paraconodonts are useful biostratigraphically. P reviously proposed protoconodont-paraconodont biozones in Hunan are revised and correlated with recently revised trilobite biozones, as well as with p rotoconodont-paraconodont and trilobite biozones in North China. Twenty-six species and seven conditionally identified species belonging to 13 genera are described. Among these, two genera (Huayuanodontus and Yongshunella) an d two species (Westergaardodina elegans and Yongshunella polymorpha) are ne w. This study has special interest for Cambrian biostratigraphy because the two studied sections are global stratotype candidates for the Middle-Upper Cambrian series boundary. The level of the Upper-Middle Cambrian Series bo undary, as currently recognized in China (at the base of the Linguagnostus reconditus Trilobite Biozone) is well marked in the paraconodont succession and can be traced into the Swedish standard succession using these fossils . By contrast, another level recently proposed as a potential global Middle -Upper Cambrian Series boundary level, the base of the Glyptagnostus reticu latus Trilobite Biozone, does not coincide with any marked change in the Hu nan conodont species succession useful for local and regional correlation.