Caenagnathus
Caenagnathus ('recent jaw') is a genus of caenagnathid oviraptorosaurian dinosaur from the late Cretaceous period (Campanian stage; ~75 million years ago). It is known from partial remains including lower jaws, a tail vertebra, hand bones, and hind limbs, all found in the Dinosaur Park Formation of Alberta, Canada. "Caenagnathus" weighed about a maximum of . Description. "Caenagnathus" was a large oviraptorosaurian, with some specimens suggesting it achieved sizes comparable to its relative "Anzu". Like "Anzu", it had a toothless lower beak that was shallower in depth than those of elmisaurines. It also shared with "Anzu" less gracile proportions than those  of elmisaurines. Like all oviraptorosaurs, it would most likely have possessed a coat of feathers. Classification. This dinosaur has a confusing history. In 1936, a set of jaws (CMN 8776) were found, and later given the name "Caenagnathus", meaning 'recent jaw'; they were first thought to be those of a bird. In 1988, a specimen from storage since 1923 was discovered and studied. This fossil was used to link the discoveries of several fragmentary oviraptorosaur species into a single dinosaur, which was assigned to the genus "Chirostenotes", originally named for a pair of hands that were long considered to come  from the same animal as "Caenagnathus". Since the first name applied to any of these remains was "Chirostenotes", this was the only name recognized as valid for many years. However, Senter and Parrish (2005) doubted the synonymy of "Caenagnathus" with "Chirostenotes", noting that the maxillary remains included in the "Epichirostenotes" holotype didn't overlap with CMN 8776. A cladistic analysis of Coelurosauria by Senter (2007) found "Caenagnathus" to fall basally within Caenagnathoidea, while "Chirostenotes" fell as a derived taxon related to "Elmisaurus". The status and relationships of "Caenagnathus" to other caenagnathid oviraptorosaurians began to be resolved with the discovery of  more complete specimens in 2014 and 2015. The description of "Anzu wyliei" in 2014 represented the first nearly complete caenagnathid, and helped to clarify the differences between the more fragmentary specimens. Phylogenetic analyses found "Caenagnathus collinsi" to be more closely related to "Anzu" than to "Chirostenotes". A second species which had previously been referred to "Caenagnathus", "Caenagnathus" "sternbergi", was found to be the sister taxon to the grouping of "Anzu" and "Caenagnathus" in one 2014 analysis. In 2015, new fossil remains were found to belong to "Caenagnathus collinsi". These appeared to be intermediate in size and anatomy between the smaller  Chirostenotes and the larger "Anzu", lending support to their hypothesized relationships. These bones can be distinguished from "Chirostenotes" and contemporary ""Leptorhynchos" elegans" by features of the limbs, specifically the hand and metatarsals. A new "Chirostenotes" specimen described by Funston and Currie (2020) preserving a mandible provides further evidence that "Caenagnathus" is a distinct genus from "Chirostenotes" despite both taxa being part of the Caenagnathidae.