Exceptionally preserved radiodont arthropods from the lower Cambrian (Stage 3) Qingjiang Lagerstätte of Hubei, South China and the biogeographic and diversification patterns of radiodonts

The Cambrian (Series 2, Stage 3) Qingjiang Lagerstätte of South China is one of the most diverse Burgess Shale-type deposits around the world, yielding abundant non-biomineralized fossils. Radiodonta, a taxonomically and ecologically diverse stem-euarthropod group, has been generally thought to represent the largest consumers in early Palaeozoic marine ecosystems. Here we describe several new radiodont specimens from the Qingjiang Lagerstätte assigned to various groups, including Stanleycaris qingjiangensis sp. nov., a new type of hurdiid head carapace, one possible Hurdia carapace, and two partial appendages with uncertain affinities. These specimens not only extend the geographic and stratigraphic range of these taxa, they also illuminate the diversity of radiodonts (in particular hurdiids) in their early evolutionary history. Radiodont palaeobiogeographic patterns are visualized using network analysis. Laurentia and South China share many members at the genus level, Anomalocaris is the most cosmopolitan taxon, but most genera are endemic. Radiodonts show a high initial diversity that declines through the early Palaeozoic, enabling three diversification phases of radiodonts to be recognized: the thriving phase (Cambrian Series 2), declining phase (Cambrian Miaolingian) and terminal phase (Cambrian Furongian to Ordovician Floian).