First report of the hurdiid radiodont Ursulinacaris from the Cambrian Kaili Biota, South China

Abstract

Radiodonts are globally distributed from the Cambrian Series 2 to Miaolingian. However, their occurrences in South China during the Miaolingian Epoch remains limited, particularly for hurdiids, which are highly abundant in other palaeocontinents. Here, we present the first discovery of hurdiid frontal appendages from the Cambrian Kaili Biota (Miaolingian) in South China. These appendages display distinctive morphological features, including five paired spiniform endites in the intermediate region, which facilitate their assignment to Ursulinacaris cf. U. grallae. This finding expands the palaeogeographic distributions of Ursulinacaris, which was previously thought to be confined to Laurentia in Miaolingian, and reinforces the biogeographic connection between Laurentia and South China during this time interval. An analysis of radiodont biodiversity patterns in Laurentian and South China suggests a shift in their evolutionary radiation center from shallow-water environments during the Cambrian Epoch 2 to deeper-water habitats of the Miaolingian. Furthermore, the alteration of radiodont biodiversity from the Cambrian Series 2 to Miaolingian may correlate with the Redlichiid-Olenellid Extinction Carbon Isotope Excursion (ROECE).