First complete Niobe yangtzeensis Lu, 1975 (Asaphidae, Trilobita) from the Middle Ordovician of South China, and its systematic and palaeogeographic implications

Since Niobe yangtzeensis was erected in 1975, due to no complete or even cephalic specimens, the generic assignment of Niobe yangtzeensis remains controversial. Based on the new discovery of a complete specimen of Niobe yangtzeensis in Yichang of South China, this species is redescribed and its generic position assignment is clarified and confirmed. A phylogenetic analysis of Niobinae shows that each of the four genera of this subfamily (Niobe, Niobella, Proxiniobe and Gog) forms a monophyletic group, and that among which Niobe yangtzeensis belongs to the genus Niobe. The palaeogeographical distribution and environmental analysis of Niobinae, suggest that Niobella, Proxiniobe and Gog lived in a relatively deeper-water (the outer-shelf or slope) environment, while Niobe preferred a shallower water environment, such as the inner shelf.