A new radiodont from the lower Cambrian (Series 2 Stage 3) Chengjiang Lagerstatte, South China informs the evolution of feeding structures in radiodonts

Abstract

Radiodonts, a diverse clade of early Palaeozoic stem-group euarthropods, have provided critical information for understanding the evolution of this phylum, and were important constituents of marine ecosystems. The well-known Chengjiang Lagerstatte (Cambrian Stage 3, ca. 518 Ma) has yielded the highest known diversity of radiodonts of any Cambrian Konservat-Lagerstatten, and represents a crucial deposit for radiodont research. One important but generally overlooked Chengjiang radiodont taxon, previously identified as Anomalocaris sp. or Radiodont C, is herein designated as the type species of a new monotypic genus, Shucaris ankylosskelos gen. et sp. nov based on dozens of specimens. Shucaris is distinctive for its combination of several characters, including the presence of two pairs of endites on its proximalmost claw podomere, posteriorly-inward curved endites on claw podomeres 2-6, and most strikingly the coexistence of gnathobase-like structures and oral cone. New material of Ramskoeldia consimilis records the first known oral cone in this species, confirming that oral cones and gnathobase-like structures co-occur in multiple radiodont taxa. Phylogenetic analysis retrieves Shucaris as either an early diverging member of Anomalocarididae or as sister to the clade Anomalocarididae + Amplectobeluidae. Moreover, our phylogenetic analysis also supports the divergence between hurdiid and non-hurdiid radiodonts.