Cretaceous Bird Fossils of Alberta, Canada

Cretaceous birds of Alberta are poorly understood, 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. Its structure is similar to previously described ornithurine coracoids from Alberta and other localities in North America, including those belonging to the genus Cimolopteryx. A comparison of these elements indicates that the new coracoid is distinct; however, its preservation prevents complete diagnosis. A pneumatized coracoid is a defining trait of Neornithes, often associated with the presence of a pneumatic foramen. Ornithurine G does not preserve this feature. Also, CT and micro-CT scans of both pneumatic and apneumatic coracoids of modern birds show similar internal structures to Ornithine G, indicating that pneumaticity of the coracoid cannot be determined in the absence of an external pneumatic foramen. A phylogenetic analysis was unable to resolve unclear relationships between Ornithine G, Cimolopterygidae, and neornithine birds, and questions both the assignment of Lamarqueavis to the Cimolopterygidae, and the validity of the family as a whole. Isolated teeth, previously identified as avian, are more common than other avian fossils from the Late Cretaceous of Alberta, although none are associated with skeletal material. A variety of specimens ranging from Late Santonian to Late Maastrichtian in age are described in detail and categorized into morphotypes based on qualitative assessment. Numerous characters are shared between birds, non-avian theropods, and crocodilians. In particular, the shape of the crown and surface enamel features of some putative avian teeth strongly resembles those found in the jaws of extant juvenile and some fossil crocodilians. However, whereas quantitative analysis (PCA ordination) was able to separate some putative avian morphotypes from non-avian theropods, and most crocodilian teeth, many of these clusters overlapped. Variation within this sample of teeth may reflect the heterodont dentition of crocodilians, rather than avian species diversity. Reassignment of many putative avian teeth to Crocodylia has important ramifications for the identification of small, isolated teeth, and for interpreting the evolutionary history of Cretaceous birds.

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