Tremadocian (Ordovician) reclined graptolites from Baishan, North China

The Erdaopuzi section in the Baishan area of Jilin Province, northeast China, contains abundant late Tremadoc graptolites. However, there are some taxonomic controversies regarding the characters of the hand specimens that are difficult to identify. In this paper, we present our restudy of isolated graptolites from acid residue and discuss the taxonomic problems of the subgenus Clonograptus (Neoclonograptus) Zhao and Zhang. Four genera and six species were identified, including Adelograptus tenellus (Linnarsson), Ancoragraptus gracilis (Zhao and Zhang), Dictyonema sp., Psigraptus jacksoni Rickards and Stait, Psigraptus lenzi Jackson, Psigraptus arcticus Jackson. According to the significant evolution of morphological characters, two graptolite zones (from bottom to top) can be identified in ascending order in the study area, i.e. Adelograptus Zone and the Psigraptus Zone.