Description of new Permian orthocerid forms from Gufeng Formation of South China (the Yangtze Craton) and their palaeobiogeographic implications in the Palaeotethys

Orthocerids from the Upper Gufeng Formation, Guadalupian (middle Permian), from Anhui Province (China) are described for the first time in this article. The specimens are mainly Pseudorthoceratidae characterised by slender orthocones that have been studied under CT-Scan. A new genus and species have been described, Houdongoceras chaohuensis gen. et sp. nov., with seven morphotypes that presumably relate to new ones. Seventeen per cent of the specimens have epibiotic bacterial colonies associated indicating suboxic environments restating redox conditions during their deposition. This is also the first report of Permian macrofossils presenting bacterial colonies in China. This fauna is interpreted as autochthonous or parautochthonous which originally lived nektobenthically in shallow marine waters above the sediments or close to the sea bottom on the eastern margin of the Palaeotethys Ocean during the late Guadalupian faunal crisis.