No abstract

78.Dentary: (0) elongate; (1) proportionally short and deep, with maximum depth of dentary between 25% and 50% of dentary length (with length measured from the tip of the jaw to the end of the posterodorsal process); (2) extremely short and deep, with maximum depth 50% or more of dentary length. [ORDERED] Modification-Removed [ORDERED] Justification-Mandibular variation through ontogeny in has not been qualified in oviraptorosaurs, nor has the degree of intraspecific variation. This character in particular is correlated with size in caenagnathids, such that larger specimens tend show state 0, and smaller specimens tend to show state 2, with a smooth gradient between. 84. Anterodorsal margin of dentary in lateral view: (0) straight; (1) concave; (2) broadly concave. [ORDERED] Modification-Removed [ORDERED] Justification-As above, though the opposite correlation to size is shown: large specimens tend to show state 2, and small specimens tend to show state 0. 176. Manual phalanx II-2: (0) longer than II-1; (1) subequal to or slightly shorter than II-1; (2) distinctly shorter than II-1. [ORDERED] Modification-Removed [ORDERED]Justification-Caenagnathid manual proportions are highly variable, with a number of apparent reversals within clades. For example, Hagryphus giganteus, scored as character state 1 for this character, is consistently recovered as a basal caenagnathid, but within more derived caenagnathids, all three character states for this character are present, indicating that the character state can move both directions.

Our understanding of caenagnathid anatomy, diversity, and ecology has improved considerably in the past twenty years, but numerous issues still remain. Among these, the diversity and taxonomy of caenagnathids from the Dinosaur Park Formation of Alberta, Canada, have remained problematic. Whereas some authors recognize three genera, others suggest only two were present, and there is considerable disagreement about which specimens are referable to which genus. This study aims to resolve this issue by reviewing the known specimens and using osteohistology, to establish a testable taxonomic framework of Dinosaur Park Formation caenagnathids. Numerous new specimens from all regions of the skeleton provide insight into morphological variation in caenagnathids, and three morphotypes are recognized based on a combination of morphological features and body size. Osteohistology shows that representatives in each body size class are at skeletal maturity, and therefore supports the delineation of three taxa: the smaller Citipes elegans gen. nov., the intermediate Chirostenotes pergracilis, and the larger Caenagnathus collinsi, new material of which shows it rivalled Anzu wyliei in size. However, these analyses also raise concerns about the referral of isolated material to each taxon in the absence of skeletal overlap between specimens or osteohistological analysis. Caenagnathids are consistently recovered throughout the Dinosaur Park Formation interval, and two geographic clusters of increased abundance probably reflect collection and taphonomic biases. The coexistence of three taxa was apparently facilitated by differences in both adult body size and functional morphology of the dentary and pes, which suggests that caenagnathids minimized niche overlap rather than subdividing niche space. Regardless, little is known of the exact roles caenagnathids played in Late Cretaceous ecosystems. Incorporation of the new material and taxonomic framework into a phylogenetic analysis drastically improves our understanding of the relationships between caenagnathines, and sheds light on the evolution of body size in caenagnathids and its role in their diversification.

Until recently, caenagnathids were a family of oviraptorosaurs represented only by fragmentary material. As such, caenagnathid biology has never been studied in depth. A well-preserved mandible provides new information on the anatomy and dietary habits of Chirostenotes. The mandible is edentulous, has a completely fused symphysis, with sharp occlusal margins and complex lingual surfaces. Finite element analysis shows that the lingual ridges are reinforced. This suggests that they had a function in food processing. These and other features suggest adaptations for an efficient shearing mechanism, and the overall morphology is poorly adapted for durophagous behaviour. Comparisons with three groups with convergently similar mandibles, especially dicynodonts, indicate caenagnathids were capable of handling an herbivorous diet. Here, an omnivorous diet is proposed for Chirostenotes, including folivory and small prey.

New specimens from Canada confirm the presence of elmisaurines in North America