Occurrence of Sanqiaspis, Liu, 1975 (Vertebrata, Galeaspida) in the Lower Devonian of Vietnam, with remarks on the anatomy and systematics of the Sanqiaspididae

A new species of the huananaspidiform galeaspid genus Sanqiaspis is reported from the Lochkovian Si Ka Formation of northern Vietnam and is somewhat older than the previously recorded occurrences of this genus, from the Pragian Posongchong Formation of southern China. This species provides new information about the anatomy of the head shield in the Sanqiaspididae and notably provides evidence of a complete endoskeletal and dermal postbranchial wall, like in osteostracans. The various types of vertebrate assemblages defined in the Lower Devonian of China are discussed, by comparison to the vertebrate faunas hitherto recorded from the Lower Devonian of Vietnam, and it is suggested that their composition is strongly influenced by environmental factors.