Innovatiocaris, a complete radiodont from the early Cambrian Chengjiang Lagerstätte and its implications for the phylogeny of Radiodonta

Abstract: The Palaeozoic radiodonts are important for understanding the evolution and ecology of early euarthropods. However, complete radiodont fossils are very rare, despite their central roles in understanding radiodont palaeobiology. Here we describe Innovatiocaris maotianshanensis gen. et sp. nov. in detail based on an iconic complete radiodont specimen from the early Cambrian Chengjiang Lagerstätte of China. The head of I. maotianshanensis has a pair of stalked eyes, an ovate dorsal sclerite, a pair of frontal appendages composed of 11 distal articulated podomeres bearing spiky endites with only anterior auxiliary spines, and a putative triradial oral cone. The body possesses six anterior pairs of small differentiated neck flaps and ten posterior pairs of trunk flaps, with soft tissues including alimentary canal and musculature preserved. The tail includes a tail fan comprising three pairs of lateral blades and a pair of very long furcae. Another two new species, Innovatiocaris? sp. and I.? multispiniformis sp. nov., are established based on the frontal appendages with different numbers of anterior auxiliary spines and are tentatively assigned to Innovatiocaris. Phylogenetic analysis retrieves Innovatiocaris as either a basal member of Hurdiidae or early-branching species of the non-hurdiid clade. Thus, Innovatiocaris provides new insights into the radiodont phylogeny and illuminates the early diversification of Radiodonta.