Silurian and Devonian jawless craniates (Galeaspida, Thelodonti) and their habitats in China

A review of fossil jawless craniate studies in China concerns mainly galeaspids and thelodonts. The pattern and structure of the sensory-line system in galeaspids differs greatly from that of osteostracans or heterostracans. The Order Macrothyraspidida is a monophyletic group within the Galeaspida, defined by an important synapomorphy, i.e., the cephalic shield with a pair of latero- or medium dorsal fenestrae. The habitat of fossil jawless craniates in China might have been littoral to neritic, on the basis of associated marine fossils and the analysis of fish-bearing sedimentary facies. They are considered to be euryhaline animals and not solely fresh water .