On the Diversity and Morphology of Anserini (Aves: Anatidae) from the Late Miocene of Western Mongolia

New previously unstudied geese bones (two coracoids and tarsometatarsus) are described from the late Miocene locality Hyargas Nuur 2 in Western Mongolia. A tarsometatarsus, previously unknown for Anser devjatkini Kurochkin, 1971, indicates close phylogenetic relationships of this extinct species with modern grey geese. Previously noted similarity with white geese is treated as plesiomorphic. Morphological transition from white to grey geese thus was associated with changes in locomotor specialization of the hind limb (swimming versus running adaptations). Two coracoids are different from those in modern Anser and Branta, but are close to “Branta” woolfendeni Bickart, 1990 from the late Miocene of Arizona (USA), from which they differ in their bigger size. These latter finds represent a distinct extinct unnamed genus of geese, which was widespread across Central Asia and North America in the late Miocene. Late Miocene evolution and paleogeography of geese is further discussed. The remarkable diversity of geese at the Hyargas Nuur locality (at least 3‒4 species) may be explained by wintering of these birds on the large lakes of Central Asia.