Early-Middle Ordovician brachiopod dispersal patterns in South China.

Paleobiogeographic patterns of the brachiopod faunas before and during the first radiation of the Great Ordovician Biodiversification Event (GOBE) in South China at 6 different localities from the upper Jiangnan Slope to the vast area of the Upper Yangtze Platform show several interesting features. First, the initial brachiopod diversity acme was accompanied by both high origination and extinction rates. Second, no significant changes took place in the taxonomic composition and paleobiogeographic pattern of the brachiopod fauna during the radiation at 5 of the 6 localities studied except the near shore locality, where the first brachiopod radiation was much later than at other localities and was marked by a dramatic increase in endemic constituents. Third, orthides were the predominant brachiopod group during the radiation, and regional brachiopod taxa played a significant role in defining the paleobiogeographic pattern of the radiation. Fourth, the first brachiopod radiation was associated with 3 major pulses of onshore migration from the upper Jiangnan Slope through the central Upper Yangtze Platform to the near shore settings of the platform, with the middle pulse being the most significant. Finally, paleogeographic dispersal took place in both onshore and offshore directions, although the onshore expansion was more prominent; several key brachiopods, such as Paralenorthis, Nocturnellia, Protoskenidioides, Nereidella, Euorthisina and Yangtzeella, first appeared on the upper Jiangnan Slope and later formed distinct, and taxonomically diverse, communities on the Upper Yangtze Platform. The paleogeographic dispersal of brachiopods is considered to be closely related to the tectonic evolution of the Qianzhong Arch.