MIOCENE MACROFLORAS FROM ARGENTINA

The Miocene epoch (23.03–5.33 Ma) is a critical time interval in the evolution of modern vegetation because the continents had nearly assumed their current positions. Major tectonic, oceanic, and geological events altered environments globally during its duration. Data for modeling these changes come from many sources, including paleogeographical reconstructions (land-sea distribution, ocean gateways, and intercontinental seas/seaways), isotopes (δ¹⁸O and δ¹³C), and the marine and terrestrial fossil records. Knowledge of global changes during the Miocene is mainly supported by data gathered from the Northern Hemisphere (NH); in contrast, few records from the Southern Hemisphere (SH) have influenced our understanding of the Miocene world. Assuming that data from the NH can accurately represent Miocene biomes globally ignores that the NH and SH are quite different in geography, land-water ratio, topography, and climate. These differences add uncertainty to the already known NH bias in fossil collection. The Southern Hemisphere—particularly Patagonia, the southernmost portion of South America —was affected during the Miocene by several significant events, including the final stages in the establishment of the Antarctic Circumpolar Current through the opening of the Drake Passage, the “Entrerriense Sea” transgression, the presence of the permanent ice sheet on Antarctica, and the uplift of the Andes. These regional forces drove aridification and cooling during the Miocene, which spurred a transition from forest to shrubland east of the Andes, causing the extinction of plants requiring a warmer, less seasonal climate and/or more moisture. Here, we compare a suite of eleven Argentinean Miocene macrofloras in a latitudinal gradient (25° to 53° S) to determine their taxonomical, biogeographical, and paleoclimatic similarities and differences.