New caenagnathid (Dinosauria: Theropoda) specimens from the Upper Cretaceous of North America and Asia

Abstract

New specimens of caenagnathid theropods are described from the Judith River Formation (Campanian) of southern Alberta, the Hell Creek Formation (Maastrichtian) of South Dakota, and the Bissekty Formation (Turonian) of Uzbekistan. With the exception of the Hell Creek specimen, and a vertebra from Alberta, all are from the symphysial regions of the lower jaws. Caenagnathids are rare and poorly known animals, and the described fossils preserve heretofore unknown features, including vascular grooves and foramina in the symphysial region, and the pattern of overlapping sutures between jaw elements. Most of the new specimens are different from the holotype of Caenagnathus collinsi Sternberg and may represent the second described species, Caenagnathus sternbergi. The two jaws from the Bissekty Formation are the first oviraptorosaurian jaws described from Uzbekistan and represent a new genus and species anatomically closer to Caenagnathus than to central Asian forms like Oviraptor, Conchoraptor and Ingenia. There are at least five characters that distinguish caenagnathid and oviraptorid jaws, but it is concluded that the length of the symphysial region must be used with caution. Jaw anatomy supports the idea that oviraptorids were well adapted for eating eggs, although their diet was probably not restricted to one food type.

Osteology of Khaan mckennai (Oviraptorosauria: Theropoda)

“…3B, C, 5B). The mandible of Khaan mckennai preserves the bizarre anteroposterior shortening present in all other oviraptorids, which lack the elongation of other theropods, caenagnathids, and basal oviraptorosaurs such as Incisivosaurus gauthieri and Caudipteryx zoui (Sternberg, 1940;Barsbold, 1981;Currie et al, 1993;Sues, 1997;Ji et al, 1998;Balanoff et al, 2009). Oviraptorids also share a dorsoventrally high coronoid eminence with corresponding surangular spine that extends anteriorly into (but not completely dividing) the enlarged heart-shaped mandibular fenestra.…”

“…The presence of these foramina, as in the premaxillae, suggests that the dentary was covered by a keratinous rhamphotheca in life similar to what is seen in modern birds and turtles (Bubien-Waluszewska, 1981). These foramina are present in other oviraptorids and caengnathids as well as the basal forms of Incisivosaurus gauthieri and Caudipteryx zoui (Currie et al, 1993;Ji et al, 1998;Osmó lska et al, 2004;Xu et al, 2003). Such structures cannot be distinguished in Gigantoraptor erlianensis.…”

“…The basal taxa Incisivosaurus gauthieri and Caudipteryx zoui are almost completely horizontal. Microvenator celer has a pronounced bend anteriorly in its dentary (Makovicky and Sues, 1998), but all of the observed caenagnathids have an almost horizontal dentary (Currie et al, 1993). All oviraptorids have some degree of downturn at the anterior margin of the dentary.…”

“…The posterior end of the surangular tapers along the articulation with the articular, ending just under the mandibular articulation surface with the cranium. The surangular does not contribute to the mandibular articulation and is not fused into a surangular/ articular/coronoid complex as in caenagnathids (Currie et al, 1993). The posterior region of the lateral surface of the surangular has a shallow fossa that is longitudinally oriented for the attachment of the adductor muscles.…”

“…We follow Sues (1997) for caenagnathid taxonomy. That paper gives the definition for Caenagnathidae as ''Chirostenotes pergracilis, Chirostenotes elegans, an as yet unnamed large caenagnathid (Currie et al, [1993]; Triebold and Russell, 1995), 'Elmisaurus rarus,' Caenagnathasia martinsoni, and the most recent common ancestor of the aforementioned taxa'' (Sues, 1997). Oviraptoridae is the largest of the nodebased groups and includes a wide variety of taxa.…”