Abstract
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.
Highlights
Nothofagus Blume belongs to the monogeneric family Nothofagaceae and includes 43 extant species of trees (Christenhusz & Byng, 2016) grouped in four monophyletic subgenera (Hill & Read, 1991)
The extant vegetation of the Río Turbio area corresponds to an ecotone between the Patagonian cool temperate rainforest dominated by Nothofagus pumilio (Poepp. & Endl.) Krasser (Lenga) followed by Nothofagus antarctica (G.Forst.) Oerst. (Ñire) (León et al, 1998; Cavallaro, 2006) and the steppe dominated by shrubs and herbs
The genus Nothofagus is divided into four monophyletic subgenera Brassospora Nothofagus, Lophozonia and Fuscospora, based on pollen, leaf and reproductive morphology (Dettman et al, 1990; Hill & Read, 1991)
Summary
Nothofagus Blume belongs to the monogeneric family Nothofagaceae and includes 43 extant species of trees (Christenhusz & Byng, 2016) grouped in four monophyletic subgenera (Hill & Read, 1991). In South America, Nothofagaceae is represented by 10 species, most of them deciduous, distributed in the Andean Region from 33° to 56° S latitude, with the northern limit determined by the seasonally arid conditions of the Mediterranean climate of central. 37o south in both, Chile and Argentina, Nothofagus occurs in two broad types of forests: temperate rainforests on climatically favourable sites, generally associated with Maytenus magellanica, Drimys winteri, Pilgerodendron uviferum and Embothrium coccineum among others and, a pure or nearly pure Nothofagus forests on less favourable sites referred to as Patagonian or Subantartic Nothofagus forests (Veblen et al, 1996). The extant vegetation of the Río Turbio area corresponds to an ecotone between the Patagonian cool temperate rainforest dominated by Nothofagus pumilio The extant vegetation of the Río Turbio area corresponds to an ecotone between the Patagonian cool temperate rainforest dominated by Nothofagus pumilio (Poepp. & Endl.) Krasser (Lenga) followed by Nothofagus antarctica (G.Forst.) Oerst. (Ñire) (León et al, 1998; Cavallaro, 2006) and the steppe dominated by shrubs and herbs.
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