A Revision of the Palaeocene–Eocene Mongolian Presbyornithidae (Aves: Anseriformes)

Remains of the stem anseriforms Presbyornithidae dominate among the avian material from the Tsagaan-Khushu locality in southern Mongolia (Naran-Bulak Formation; upper Paleocene–lower Eocene). Revision of the materials previously attributed to Presbyornis showed that they actually belong to two taxa of Presbyornithidae plus one or two taxa of stem Phoenicopterimorphae. The relatively large presbyornithid is morphologically similar to smaller specimens of Presbyornis pervetus Wetmore, 1926 from the lower Eocene of the United States. Another small form described here as Bumbalavis anatoides gen. et sp. nov. is morphologically more advanced than Presbyornis. Thus, the Mongolian materials do not confirm the presence of significant body size dimorphism in Presbyornis. Stem Phoenicopterimorphae from Tsagaan-Khushu are tentatively assigned to Juncitarsidae, to which the holotype of Presbyornis mongoliensis Kurochkin et Dyke, 2010 also belongs.