A New Pleistocene bird assemblage from the Southern Pampas (Buenos Aires, Argentina)

In the present paper we report the most complete fossil avifauna from the southern cone of South America. The specimens here described were collected in the Paso Otero locality, at the middle stream of the Quequén Grande River, Pampean Region (Buenos Aires Province, Argentina). The fossiliferous levels belong to the La Chumbiada Member of Luján Formation (37,800 ± 2300 yr BP, late Pleistocene). The assemblage is represented by 60 specimens belonging to at least 22 taxa. The radiocarbon age indicates that Paso Otero birds represent the oldest late Pleistocene avifauna known from the South American continent and the first coming from a clear interstadial event (MIS3). Available evidence indicates similar environmental conditions during the MIS3 interstadial in the Pampean Region of Argentina and the post-Last Glacial Maximum stadials in southeastern Brazil. The absence of significant extinction events in the latest Pleistocene–early Holocene avifaunas of Brazil and Argentina suggests that the main avifaunal composition along southeastern continental lowlands may not be affected by the cyclic retraction and extension of open environments. On the contrary, the fossil record of Peru and Ecuador demonstrates that a large number of taxa, including aquatic and predatory-scavenger birds, have gone extinct along Andean environments at the Pacific coast, and late Pleistocene climatic oscillations may have played a more dramatic impact in these avian communities.