1． Institute of Geology，Chinese Academy of Geological Sciences，Beijing 100037，China 2． Jehol Paleontological Museum，Chengde 067000，Hebei，China

A new pterosaur Archaeoistiodactylus linglongtaensis gen． et sp． nov． is erected based on an incomplete skeleton with a partial skull and lower jaw． The new taxon is characterized by circular tooth sockets of anterior mandibular teeth，the anterior teeth of the upper jaw bearing posteriorly directed crowns，a relatively short metacarpus，and wing phalanges 2 and 3 and the tibia subequal in length． It possesses some plesiomorphic characters such as short metacarpals and circular tooth sockets． The pointed jaw tip present in the new taxon indicates that the expanded jaw tips of later istiodactylids are a derived character state，and the new taxon represents the first istiodactylus-like pterosaur found from the pre-Late Jurassic deposits，which provides a key role in our understanding the origin and evolution of the known istiodactylid pterosaurs． Archaeoistiodactylus is regarded as the ancestor form of the known istiodactylid pterosaur．