New Material Of Stegosaurs From The Lower Cretaceous Luohandong Formation Of The Ordos Basin,Inner Mongolia

Stegosauria is a clade of thyreophoran 'armoured' ornithischian dinosaurs known from Middle Jurassic to Early Cretaceous strata worldwide.They are characterized by the possession of two parasagittal rows of plates and spines that extend from the neck to the end of the tail,relatively small skull,four feet to walk,the neural arch apparently high than the centrum.They are devied into Stegosauridae and Huayangosauridae.The Early Cretaceous Zhidan Group in the northern Ordos Basin,Inner Mongolia,yields a large number of tetrapods,including turtles,choristoderes,crocodyliforms,psittacosaurs,stegosaurs,ankylosaurs,theropods,birds and primitive mammals.A well-preserved stegosaurian sacrum with paired ilia,dorsal vertebrae,scapula,dermal plate and dermal spine found from the Luohandong Formation,a middle-upper unit of Zhidan Group is referred to Wuerhosaurus ordosensis.This new material gives some additional characters on the pelvic girdle in Wuerhosaurus ordosensis,such as both concave anterior margin and concave medio-posterior margin of the supra-acetabular flange,base of dermal spine showing rhombic in proximal outline and obliquely offseting that the proximomedial margin expands asymmetrically,rhombic and transversely narrowed in cross-section,with prominent tapered edges along its anterior and posterior sides.Comparing Wuerhosaurus ordosensis to W.homheni that was known from Xinjiang Uygur Autonomous Region,the author points out the differences between the two species:(1)a relatively short anterior iliac process in W.ordosensis;(2)the anterior iliac process with arched posterior portion of the dorsal margin in W.ordosensis,while anterior iliac process with nearly parallel dorsal and ventral margins in W.homheni;(3)the relatively small angle between anterior iliac processes and midline in W.ordosensis;(4)acromial process of W.ordosensis in the lateral view,showing a triangle-shaped while rectangle-shaped in W.homheni;(5)blade of scapula in W.ordosensis distally expanded instead of parallel sided in W.homheni.Those characters further provide the evidences that W.ordosensis and W.homheni are distinct species.Psittacosaurus faunas distribute in Early Cretaceous of north China,including Shandong,Liaoning,Inner Monglia,Gansu and Xinjiang.Comparison of vertebrate fossils from the Ordos Basin,Junggar Basin and Mazongshan region in Early Cretaceous,the vertebrates in Ordos Basin has more close connection with Junggar Basin than with Mazongshan region.