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Perisyncolporites pokornyi Germeraad, Hopping & Muller, erected to group fossil pollen similar to Malpighiaceae, includes a wide variety of pollen-forms with a complex aperture distribution, more or less concordant with the sides of a hexagon. The extant clades most closely related to the fossil forms of the Río Turbio Formation (Tetrapteroids and Stigmaphylloids) are today distributed in tropical and subtropical regions of South America, reaching up to the 35ºS. The only extant species distributed closer to the studied area, and that, in turn, represents the world's southernmost penetration of the family (Gallardoa fischeri Hicken, reaching the 42°S), is morphologically unrelated to the studied fossils. The foliar impression is similar to those recognized previously in the Río Pichileufú locality, Río Negro Province (Mascagnia sepiumoides Berry, Tetrapteris precrebrifolia Berry), and also in the Río Turbio Formation (Tetrapteris precrebrifolia Berry). The present results support earlier hypotheses that suggest a major penetration of Neotropical lineages into the southernmost latitudes during the Eocene as well as a possible migration to Australia via Antarctica, at least of those perisyncolporate-related forms.

A major climate shift took place about 40 Myr ago—the Middle Eocene Climatic Optimum or MECO—triggered by a significant rise of atmospheric CO2 concentrations. The biotic response to this MECO is well documented in the marine realm, but poorly explored in adjacent landmasses. Here, we quantify the response of the floras from America’s southernmost latitudes based on the analysis of terrestrially derived spores and pollen grains from the mid-late Eocene (~46–34 Myr) of southern Patagonia. Robust nonparametric estimators indicate that floras in southern Patagonia were in average ~40% more diverse during the MECO than pre-MECO and post-MECO intervals. The high atmospheric CO2 and increasing temperatures may have favored the combination of neotropical migrants with Gondwanan species, explaining in part the high diversity that we observed during the MECO. Our reconstructed biota reflects a greenhouse world and offers a climatic and ecological deep time scenario of an ice-free sub-Antarctic realm.

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