A New Istiodactylid Pterosaur From The Early Cretaceous Of Chaoyang City,Liaoning Province

Istiodactylids are advanced pterodactyloids.They are characterized by rhombic teeth with lancet-shaped crowns,long skulls with short pre-antorbital portions of the rostrum,and nasoantorbital fenestrae occupying over 50%of the total skull length and height.Four genera and five species had been reported until a distinct species was named in 2019 and described in this Dissertation,namely Istiodactylus latidens,Liaoxipterus brachyognathus,Nurhachius ignaciobritoi,Istiodactylus sinensis and Longchengpterus zhaoi.All istiodactylid pterosaurs are from western Liaoning(northeastern China)with the exception of Istiodactylus latidens,which is from the Isle of Wight(southern England).Also,three more taxa suggested to have close relationship with istiodactylids come from western Liaoning:Haopterus gracilis,Hongshanopterus lacustris,and Archaeoistiodactylus linglongtaensis.In 2019,the second species of Nurhachius,N.luei,was established based on a complete skull with mandibles and some cervical vertebrae by the author of this Dissertation and his collaborators.Many isolated fish elements are also revealed by CT scan.The holotype specimen of N.luei was found from the lower part of Jiufotang Formation of western Liaoning,while the type species of this genus N.ignaciobritoi was from the upper part of Jiufotang Formation.A revised diagnosis of the genus Nurhachius is provided,being this taxon characterized by slight dorsal deflection of the palatal anterior tip;orbit piriform;craniomandibular joint located under the anterior margin of the orbit;dentary symphysis about one-third the length of the mandible;dentary symphysis with gradual taper of the lateral margins;triangular,laterally compressed teeth lacking carinae;crowns with both labial and lingual slight concavities;slight constriction between tooth crown and root.In order to explore the phylogenetic position of Nurhachius luei among Istiodactylidae,phylogenetic analysis is performed by TNT.The result shows that Nurhachius luei belongs to genus Nurhachius.Haopterus gracilis and Hongshanopterus lacustris are closely related to Istiodactylidae.The analysis also supports Archaeoistiodactylus linglongtaensis is closely related to Darwinoptera,not Istiodactylidae.At the same time,the author of this Dissertation discusses the feeding habits and the evolutionary relationship of genus Nurhachius by the results of CT scan and the horizons of two species of this genus.