Southern beech (Nothofagaceae) fossil leaves from the Río Turbio Formation (Eocene–?Oligocene), Santa Cruz Province, Argentina.

Around one hundred specimens of fossil leaves are described herein and referred to 6 fossil-species and two taxonomic units of Nothofagaceae from the Paleogene Rio Turbio Formation, Santa Cruz Province, Argentina. These are: Nothofagus simplicidens , Nothofagus variabilis , Nothofagus lanceolata , Nothofagus subferruginea , Nothofagus dicksoni , Nothofagus sp. with Nothofagus cf. obliqua and Nothofagus magelhaenica reported for the first time for the unit. They were recorded throughout the unit, but they are fairly more abundant in the upper member of the Rio Turbio Formation where they reach the 68% of the overall assemblage. The observed increasing trend in Nothofagus abundance throughout the unit coincides with the beginning of the flora turnover that characterized Patagonian ecosystems from the Late Eocene onwards and it is in agreement with the marked global cooling trend of the terminal Paleogene.