An ornithurine bird coracoid from the Late Cretaceous of Alberta, Canada

摘要

The Cretaceous birds of Alberta are poorly known, as skeletal elements are rare and typically consist of fragmentary postcranial remains. A partial avian coracoid from the upper Campanian Dinosaur Park Formation of Alberta, Canada, can be referred to the Ornithurae, and is referred to here as Ornithurine G (cf. Cimolopteryx). Its structure is similar to previously described ornithurine coracoids from Alberta and other localities in North America, particularly those belonging to the genus Cimolopteryx. A comparison of these elements indicates that the new coracoid is distinct; however, its preservation prevents complete diagnosis. As other Cimolopteryx are Maastrichtian in age, Ornithurine G (cf. Cimolopteryx) also represents the earliest occurrence of a Cimolopteryx-like anatomy. A pneumatized coracoid is a diagnostic trait of Neornithes, identified by the presence of a pneumatic foramen. Ornithurine G (cf. Cimolopteryx) does not preserve this feature. CT and micro-CT scans of both pneumatic and apneumatic coracoids of modern birds show similar internal structures to Ornithurine G (cf. Cimotopteryx), indicating that pneumaticity of the coracoid cannot be determined in the absence of an external pneumatic foramen. A comparison between members of Cimolopterygidae, including Cimolopteryx and Lumarqueavis, raises questions about the assignment of Lamarqueavis to the Cimolopterygidae, and the validity of this family as a whole.