Spiny chondrichthyan from the lower Silurian of South China

Modern representatives of chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes and tetrapods) exhibit contrasting skeletal anatomy and development that underscore the distant evolutionary split of the two clades. Recent work on upper Silurian and Devonian jawed vertebrates has exposed similar skeletal conditions that blur conventional distinctions between osteichthyans, chondrichthyans and their jawed gnathostome ancestors. Here we describe the remains (dermal plates, scales and fin spines) of a chondrichthyan, Fanjingshania renovata gen. et sp. nov., from the lower Silurian of China that predates the earliest articulated fossils of jawed vertebrates. Fanjingshania possesses dermal shoulder girdle plates and a complement of fin spines of striking anatomical similarity to those recorded in a subset of stem chondrichthyans (climatiid 'acanthodians'). Uniquely among chondrichthyans, however, it demonstrates osteichthyan-like resorptive shedding of scale odontodes and absence of odontogenic tissues in spines. Our results identify independent acquisition of these conditions in the chondrichthyan stem group, adding Fanjingshania to an increasing number of taxa nested within traditionally-defined 'acanthodians'. The discovery of Fanjingshania provides the strongest support yet for a proposed early Silurian radiation of jawed vertebrates prior to their widespread appearance in the fossil record in the Lower Devonian.