Cranial anatomy of the small ornithischian dinosaurChangchunsaurus parvusfrom the Quantou Formation (Cretaceous: Aptian–Cenomanian) of Jilin Province, northeastern China

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 that they are sister taxa.

Tooth development, histology, and enamel microstructure in Changchunsaurus parvus: Implications for dental evolution in ornithopod dinosaurs

“…One transverse section across all dentary tooth positions (totaling 15 tooth positions) showed nine tooth positions with either a replacement tooth in the process of resorbing the root of a preceding functional tooth, or the development of a resorption pit adjacent to a functional tooth ( Fig 2A ). At the earliest stage of the tooth replacement cycle, a new tooth develops lingual to its predecessor at the level of a large foramen that opens onto the lingual surface of the dentary (also termed “special foramina” sensu [ 38 ], or “replacement foramina” sensu [ 42 ]) ( Fig 3 ), supporting the hypothesis that these foramina are the entry points of a lingually positioned dental lamina into the dentary [ 38 , 42 ]. We prefer the term “replacement foramina” for these features, because of the implied association with the dental lamina.…”

“…Sauropods, neoceratopsians, and hadrosaurids circumvented this issue by maintaining a constantly replenishing grinding or shearing surface via rapid and coordinated tooth replacement [ 1 , 24 – 27 , 52 , 53 ]. Interestingly, Changchunsaurus parvus shows evidence of continuous tooth replacement, despite maintaining a fairly uniform shearing surface of imbricated tooth crowns to pulverize tough plant material [ 42 ]. Continuous tooth replacement in these types of dentitions should typically leave gaps along the shearing surface, which would be detrimental for an herbivorous dinosaur.…”

“…The teeth of C . parvus , like those of ‘heterodontosaurids’ and early ornithopods more generally, have expanded, denticulated, and ornamented tooth crowns that are organized into a single tooth row in each jaw quadrant [ 34 , 35 , 42 , 54 ]. Moreover, the shearing surfaces of the teeth are simple, flat or gently concave surfaces supported by avascular orthodentine, bearing no resemblance to the complex occlusal plane morphology in hadrosaurid dinosaurs ( Fig 3 ) [ 2 ].…”

“…C . parvus was originally classified as ‘Ornithopoda incertae sedis ’, because this taxon possesses a number of features consistent with early ornithopods, marginocephalians, and even cerapodans more broadly [ 39 , 42 ]. Butler et al [ 54 ] noted that basal cerapodan interrelationships represented one of the most problematic and poorly understood areas of study in ornithischian phylogeny, further highlighting the importance of phylogenetically early forms, including C .…”

New small-bodied ornithopods (Dinosauria, Neornithischia) from the Early Cretaceous Wonthaggi Formation (Strzelecki Group) of the Australian-Antarctic rift system, with revision ofQantassaurus intrepidusRich and Vickers-Rich, 1999

“…The Q. intrepidus crowns differ from the subtriangular crowns (Fig. 3.3a) of noncerapodan neornithischians, e.g., Changchunsaurus parvus, Jeholosaurus shangyuanensis, Orodromeus makelai Horner and Weishampel, 1988, and Thescelosaurus neglectus-taxa that also have a prominent apicobasal swelling on the crowns, rather than a primary ridge, and fully extending apicobasal ridges on the crowns are lacking (following Jin et al, 2010). The dentary crowns of the rhabdodontids, Zalmoxes robustus and Z.…”