A loon (Aves, Gaviiformes) in the Upper Miocene of Mongolia

Loons (genus Gavia; family Gaviidae of the order Gaviiformes) are highly specialized diving birds with an incompletely understood evolutionary history. In the Early to Middle Miocene, the earliest small species of the genus Gavia were part of the warm-climate faunas of southern Europe, but as the climate cooled in the Late Miocene, loons virtually disappeared from the fossil record of Eurasia, which may be explained by a shift in their nesting range to high latitudes. The coracoid of a fossil loon from the Upper Miocene of the Hyargas Nuur 2 locality in western Mongolia described in this paper represents the oldest find of the family Gaviidae in the fossil record of Asia and the first in the continental Neogene of the region. In size, the loon from Hyargas Nuur 2 corresponds to modern G. stellata, but is morphologically closer to G. arctica and may represent an ancestral form of this modern species. This find is within the modern breeding range of G. arctica and is also interpreted as belonging to the breeding range of loons in the Late Miocene.