Diversificación y cambios de las angiospermas durante el Neógeno en Argentina

Abstract

Climate is accepted as being the main determinant of the dynamics of Neogene floral changes. The final uplift of the Andes in South America (Late Miocene-Pliocene) would have also been an important forcing factor. We present the first updated synthesis of the main changes of the Neogene flora in Argentina based on the plant fossil record. Early-Middle Miocene floras were assembled in three well supported Paleo-phytogeographic Provinces: the Neotropical, to the north, characterized by families nowadays present in the Chaco Domain (e.g. Apocinaceae, Aquifoliaceae, Cactaceae, Fabaceae, Sapotaceae, Moraceae, Anacardiaceae, Ulmaceae, Arecaceae, Amaranthaceae); the Nothofagidites, to the southwestern tip, dominated by elements of the austral forests (e.g. Nothofagaceae, Podocarpaceae, Araucariaceae, Misodendraceae, Menianthaceae, Rosaceae, Cunoniaceae); and the Transitional, in central and south-eastern Argentina, defined by a mixed of Neotropical and Austral components. By the Late Miocene-Pliocene, the area previously occupied by the Transitional Province was replaced by a new one, the ProtoEspinal/Estepa (earliest Espinal/Steppe) Province characterized by a xerophytic shrubby-herbaceous vegetation (e.g. Chenopodiaceae, Ephedraceae, Convolvulaceae, Anacardiaceae, Fabaceae, Asteraceae, Ulmaceae Celtoideae). The Neotropical and Nothofagidites Provinces remain without great variations during this interval. Pleistocene and Holocene vegetation distributions have changed extensively and repeatedly in both latitudinal and/or altitudinal gradients, which were recombined markedly in different proportions from today’s in response to the atmospheric circulation patterns, oscillations in climate, ice extent and sea level fluctuations. Pollen records suggest a transitional stage towards the present plant distributions after 4000 yr. BP south of 34º S latitude