Deanaspis, a new genus of Galeaspida (jawless stem Gnathostomata) from the Silurian of Jiangxi, China, and its evolutionary implications

A new genus and species of Galeaspida, Deanaspis longpingi gen. et sp. nov., is described from a new locality of the Silurian Xikeng Formation (from around 436 million years ago) in De'an County, Jiangxi Province. The new taxon possesses the mosaic characters of Eugaleaspiformes and Xiushuiaspidae, such as the longitudinal oval median dorsal opening in Eugealeaspiformes and the presence of the long postbranchial division of the headshied in Xiushuiaspidae. Accordingly, we erect a new family, Deanaspidae fam. nov., characterized by the longitudinal oval median dorsal opening and the long postbranchial division of the headshield covering the anterior part of the body. Our phylogenetic analysis indicates that Xiushuiaspis, Changxingaspis and Xiyuichthys form a monophyletic group, the family Xiushuiaspidae, and Deanaspidae is resolved to be the sister group of Xiushuiaspidae. Our results reveal that the long postbranchial division of Xiushuiaspidae and Deanaspidae is convergent with the inter-branchial region in polybranchiaspid galeaspids, but can be compared to the postbranchial region in some osteostracans, heterostracans and pituriaspids, and the thoracic armour of placoderms, which protects the viscera in the anterior part of the trunk. https://zoobank.org/urn:lsid:zoobank.org:pub:478B6681-44E7-4430-B91A-76E48C8FE54D