Changchunsaurus

Abstract: Ornithopods were the most important group of Cretaceous ornithischians and achieved high levels of abundance and taxonomic diversity. An understanding of the phylogeny, early evolution and diagnosis of the clade is hampered by a shortage of detailed anatomical descriptions of basal taxa. One of the most important basal ornithopod taxa discovered in recent years is Changchunsaurus parvus, from the Quantou Formation (‘middle’ Cretaceous) of Jilin Province, China, represented by excellent cranial and postcranial material. Here, we present the first description of the postcranial anatomy of the holotype specimen of Changchunsaurus and provide comparisons to other basal cerapodans and basal ornithopods. A phylogenetic analysis finds relationships amongst basal ornithopods to be extremely poorly resolved, but supports a sister-group relationship between Changchunsaurus and Jeholosaurus shangyuanensis from the Yixian Formation (late Barremian–early Aptian) of Liaoning Province, China. Numerous characters distinguish the two taxa, supporting their generic distinction. The proposed sister-group relationship suggests that an endemic clade of small-bodied bipedal ornithopods existed in north-east China during the Early to ‘middle’ Cretaceous.

Abstract: Though the dinosaur Thescelosaurus neglectus was first described in 1913 and is known from the relatively fossiliferous Lance and Hell Creek formations in the Western Interior Basin of North America, the cranial anatomy of this species remains poorly understood. The only cranial material confidently referred to this species are three fragmentary bones preserved with the paratype, hindering attempts to understand the systematic relationships of this taxon within Neornithischia. Here the cranial anatomy of T. neglectus is fully described for the first time based on two specimens that include well-preserved cranial material (NCSM 15728 and TLAM.BA.2014.027.0001). Visual inspection of exposed cranial elements of these specimens is supplemented by detailed CT data from NCSM 15728 that enabled the examination of otherwise unexposed surfaces, facilitating a complete description of the cranial anatomy of this species. The skull of T. neglectus displays a unique combination of plesiomorphic and apomorphic traits. The premaxillary and ‘cheek’ tooth morphologies are relatively derived, though less so than the condition seen in basal iguanodontians, suggesting that the high tooth count present in the premaxillae, maxillae, and dentaries may be related to the extreme elongation of the skull of this species rather than a retention of the plesiomorphic condition. The morphology of the braincase most closely resembles the iguanodontians Dryosaurus and Dysalotosaurus, especially with regard to the morphology of the prootic. One autapomorphic feature is recognized for the first time, along with several additional cranial features that diff erentiate this species from the closely related and contemporaneous Thescelosaurus assiniboiensis. Published phylogenetic hypotheses of neornithischian dinosaur relationships often diff er in the placement of the North American taxon Parksosaurus, with some recovering a close relationship with Thescelosaurus and others with the South American taxon Gasparinisaura, but never both at the same time. The new morphological observations presented herein, combined with re-examination of the holotype of Parksosaurus, suggest that Parksosaurus shares a closer relationship with Thescelosaurus than with Gasparinisaura, and that many of the features previously cited to support a relationship with the latter taxon are either also present in Thescelosaurus, are artifacts of preservation, or are the result of incomplete preparation and inaccurate interpretation of specimens. Additionally, the overall morphology of the skull and lower jaws of both Thescelosaurus and Parksosaurus also closely resemble the Asian taxa Changchunsaurus and Haya, though the interrelationships of these taxa have yet to be tested in a phylogenetic analysis that includes these new morphological data for T. neglectus.

Abstract: The Quantou Formation of Jilin Province, People's Republic of China, has recently yielded an important new fauna of ‘middle’ Cretaceous vertebrates. This fauna includes the small-bodied cerapodan ornithischian dinosaur Changchunsaurus parvus, represented by excellent cranial and postcranial material. When initially described, Changchunsaurus was hypothesed to represent one of the most basal known ornithopods; however, similarities to ceratopsians were also noted, suggesting that Changchunsaurus may be crucial to elucidating the interrelationships of basal cerapodans, one of most problematic areas of ornithischian phylogeny. Here we present a detailed description of the craniodental anatomy of Changchunsaurus, rediagnose the taxon based upon three autapomorphies, and provide comparisons to other basal cerapodans, as a foundation for future studies of basal cerapodan relationships. Changchunsaurus shows strong similarities to the Chinese Early Cretaceous cerapodan Jeholosaurus, and it is likely tha...

Abstract: Summary A new ornithopod (Changchunsaurus parvus gen. et sp. nov.) dinosaur is named and described on the basis of a specimen from the Early Cretaceous Quantou Formation at Liufangzi locality , Jilin Province, China. The specimen represents the first primitive ornithopod taxon from the Cretaceous deposits in the Songliao Basin. Changchunsaurus is an interesting ornithopod in having a combination of primitive and derived characters. It shares with some ornithopod autopomorphies: paroccipital process is crescent-shaped, the jaw articulation offsets ventral to the maxillary tooth row. It shares with euornithopods the following synapomorphies: antorbital fenestra small, external mandibular fenestra absent. However, It is believed that Changchunsaurus is also more primitive than most of ornithopods and marginocephalians in having five premaxillary teeth, a short edentulous anterior portion of premaxilla, a short diastema between premaxillary and maxilla teeth, the enamel on crowns of maxilla teeth and dentary teeth distribute symmetrically, and the premaxillary bill margin with that of the maxilla. Its jugal boss projects lateral face of the jugal. There is nubble structure on the lateral expansion of jugal, which is not described in other ornithopods. Changchunsaurus has a long predentary, which suggests it might have an immobile mandibular symphysis as in ceratopsians, and the predentary ventral process is longer than the lateral process. It is similar to derived ornithopods in the morphology of the predentary with bilobate ventral process end. Further work is needed to give precise phylogenetic relationship of the new ornithopod.