PALEOECOLOGIA y PALEOFITOGEOGRAFIA DE LAS TAFOFLORAS DEL CENOFITICO DE ARGENTINA Y AREAS VECINAS

Abstract

The currently accepted palcoecological model is discussed. Climatic type, age and specific characteristics of every taphoflora are analyzed, in the light of recently published paleoontological and stratigraphical data. Taphofloras with mixed subtropical and cold temperate plants show a wide temporal and geographical record. This makes unlikely the hypothesis of an altitudinal zonation to explain the mixture. The data suggest, instead, the existence of a stable, composite vegetal unity. It is called "Paleoflora Mixta" and is breafly characterized floristically and ecologically. To explain apparent incompatibilities it is suggested that fossil species had different ecological requirements than living ones within the same genus. The "Paleoflora Mixta" should have originated in Patagonia by Paleocene, developed in Eocene and disappeared by Oligocene. It should have formcd by in situ evolution from the warm Cretaceous vegetation of Patagonia, and by migration of subtropical species from the North and cold temperate ones from the South. In Oligocene times it was replaced by the cold temperate forest on the Andes, and probably by an herbaceous steppe in extra-andean Patagonia. lt may have persisted in the NW of Argentina with more definite Chaco features.