Discovery And Study Of Ornithopod Dinosaur Fossils From The Upper Cretaceous Nenjiang Formation In Bei’an,Heilongjiang Province,China

This study presents a newly discovered basal ornithopod dinosaur,Beiansaurus dongshengensis gen.et sp.nov.,from the Upper Cretaceous Nenjiang Formation in Bei’an,Heilongjiang Province,China.The holotype of Beiansaurus dongshengensis gen.et sp.nov.is an incomplete skeleton,including maxilla,dentary,teeth,coracoid,and vertebrae.The lithology of the Nenjiang Formation in the study area primarily consists of graygreen and brownish-red sandstone,argillaceous siltstone,and interbedded mudstone,corresponding to 3rd to 5th members of the Nenjiang formation,with an estimated age of about 82.4-79.0 Ma,assigned as early to middle Campanian.The holotype specimen of Beiansaurus dongshengensis gen.et sp.nov.exhibits two autapomorphies: 1.seven to eight nutrient foramina,with four being exceptionally large and located on the lateral surface of the dentary ramus.2.The maxillary ramus is strongly convex in lateral view and lacks nutrient foramina.It also differs from other ornithopods in several combined characteristics: the dentary teeth display more prominent primary ridges that are distinct and sharp,and a blade-like keel is present on the ventral surface of all cervical centra.A phylogenetic analysis was conducted using 255 characters of 75 individual taxa.This analysis consistently supports the placement of the Beiansaurus dongshengensis gen.et sp.nov.within the ornithopod group.Based on the available evidence,the specie appears to be closely related to Thescelosaurinae and its nearest sister taxa.However,the absence of additional material prevents a definitive phylogenetic placement of the Beiansaurus dongshengensis gen.et sp.nov.The incomplete fusion observed between most vertebral centra and their corresponding neural arches suggests that the holotype specimen of Beiansaurus dongshengensis gen.et sp.nov.was a juvenile individual at the time of demise.Considering the size of vertebrae and comparative assessment with ornithopod skeletons,it is reasonable to classify Beiansaurus dongshengensis gen.et sp.nov.as belonging to the group of small-sized basal ornithopods that inhabited northeastern China during the Late Cretaceous.The analysis also indicates that Beiansaurus dongshengensis gen.et sp.nov.is part of a unique group of early neornithischian dinosaurs found in Asia.Specifically,it reveals the presence of a clade comprising Changchunsaurus parvus,Haya griva,and Beiansaurus,which is positioned within the Thescelosaurinae subfamily within the taxonomic group Parksosauridae.The discovery and study of this new ornithopod dinosaur from the Nenjiang Formation represents a significant contribution to the paleontological importance of the region.