A new Cretaceous bird from the Maastrichtian La Colonia Formation (Patagonia, Argentina)

Abstract

The distal end of a left ulna found in the southeastern margin of the Somún Curá Plateau, Chubut Province (Argentina), was collected from the Maastrichtian (Upper Cretaceous) of the La Colonia Formation. Based on the torsion and the cylindrical section of the shaft, the complete development of both condyles, and the distal extension of the tuberculum carpale, we suggest a possible neornithine identity. Besides, an overall resemblance with Anseriformes, particularly with Presbyornithidae and Anserinae, is based on the sub-rounded shape of the caudal margin of the condylus dorsalis and the wide angle of confluence with the facies ventralis of the shaft, the rounded facies dorsalis at the distal end, the well-marked incisura tendineus, the wide and shallow incisura tuberculum carpale, and the large tuberculum carpale. The large size of the fossil and the presence of certain distinctive characters, such as the robustness of the tuberculum carpale, which is parallel to the shaft, and the slightly greater distal extension of the condylus dorsalis, suggest that this specimen belongs to a new taxon. If correctly identified, this ulna could be the first report of a neornithine bird from the La Colonia Formation.