A caenagnathid oviraptorosaur metatarsal from the Mesaverde Formation (Campanian), Wyoming

A well-preserved left theropod metatarsal I from the Campanian Mesaverde Formation of Wyoming is described and identified as belonging to a caenagnathid, representing the first occurrence of this clade from the formation. The specimen is unique in being relatively small, but featuring a suite of characters (triangular shaft, less constriction between the shaft and the distal condyle, spherical distal condyle) that are seen in larger examples of Caenagnathidae such as Anzu wyliei or “Macrophalangia canadensis”. This suggests that the previously-observed differences in metatarsal I between small and large caenagnathids are not solely the result of allometry, but may represent phylogenetically informative variation. Although limited, this new specimen lends some support to the hypothesis that “Macrophalangia canadensis” does not represent a large Chirostenotes pergracilis. Furthermore, the specimen is important in establishing the presence of caenagnathids within the Mesaverde Formation fauna, in which theropod remains are poorly known.