An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada

Relatively little is known the diversity of Late Cretaceous ornithurines, and it has generally been assumed that the ornithurine sister taxon, the Enantiornithes, were the dominant birds in Late Cretaceous continental ecosystems. Here, an ornithurine-dominated avifauna is described from the terrestrial Belly River Group (Campanian, Upper Cretaceous) of southern Alberta. On the basis of the most common element, the coracoid, eight species can be identified; all represent ornithurines. More precise identifications are hindered by the fragmentary nature of the material, but some of the forms described here resemble Cretaceous birds known from elsewhere in North America and Asia. The Judithian birds show considerable size disparity; a coracoid from the Irvine mammal locality belongs to a sparrow-sized bird, making it one of the smallest known Cretaceous birds, while the peacock-sized Palintropus is among the largest birds known from the Cretaceous. Surprisingly, no enantiornithine fossils were identified. These fossils show that the Ornithurae had diversified considerably by the end of the Campanian, and that they were the dominant birds in some North American ecosystems. The diversification of the Ornithurae towards the end of the Cretaceous could help explain how this clade managed to survive the end Cretaceous mass extinction.