A swan-sized anseriform bird from the late Paleocene of Mongolia.

The early evolutionary history of waterfowl (Anseriformes) is poorly understood. Aside from the morphologically aberrant Presbyornithidae, the only other known early Paleogene anseriform taxon is Anatalavis oxfordi from the early Eocene of England. Here, I describe two bones from the late Paleocene of southern Mongolia (localities Naran-Bulag and Tsagaan-Khushuu), which belong to a very large swan-sized swimming waterfowl (Anseriformes) and are described as Naranbulagornis khun, gen. et sp. nov. This is the first non-presbyornithid anseriform bird found in the early Paleogene (Paleocene through early Eocene) of Asia and one of the few currently known Paleocene birds from Central Asia. It is also the largest volant bird from the Paleogene of Asia. Naranbulagornis khun documents a mosaic of autapomorphic and plesiomorphic features that are otherwise present in modern Anhimidae, Anseranatidae, and Anatidae, indicating a greater morphological diversity of early Cenozoic anseriforms than previously thought. The new taxon is morphologically closer to Anatoidea than to Presbyornithidae and represents the earliest global evidence of a spatial coexistence between presbyornithids and other basal waterfowl during the early Paleogene. [ABSTRACT FROM AUTHOR]