Response of plant diversity to Miocene forcing events: the case of Patagonia

BARREDA, V. D.; PALAZZESI, L

Paleobotany and Biogeography: A Festschrift for Alan Graham in His 80th

Missouri Botanical Garden

Lugar: Missouri; Año: 2014; p. 1 - 25

Humid forested communities from eastern Patagonia were replaced by open habitat ecosystems sometime during the mid Miocene. This major turnover involved a significant physiognomic replacement (i.e. a tree-dominated biome by a shrub-dominated biome), although its associated shift in plant diversity through this time interval has never been quantitatively surveyed. Here, we explore for the first time the diversity patterns of the Miocene spore-pollen records from southern South America. Quantitative results reveal significant differences in the abundance and particularly in the diversity of the major plant groups from the early to the late Miocene. Early Miocene spore-pollen assemblages indicate a highly diverse forested ecosystem (rarefied richness at 200 specimens: 64) dominated by podocarps, araucarians, southern beeches and ferns, with patches of open-habitat species. By the late Miocene, this was followed by a markedly different, lower diversity community (rarefied richness at 200 specimens: 22) dominated by arid-adapted shrubs of amaranths and Ephedra. Ferns and conifers were the most affected groups. Angiosperms slightly declined in diversity yet became dominant for the first time in the Miocene, probably because of their evolutionary adaptability to disturbed habitats, which may have been, in part, responsible for the success of angiosperms overall.