A snapshot of mid Eocene landscapes in the southern Central Andes: Spore-pollen records from the Casa Grande Formation (Jujuy, Argentina).

The southern Central Andes-or Puna-now contains specialized plant communities adapted to life in extreme environments. During the middle Eocene (~40 Ma), the Cordillera at these latitudes was barely uplifted and global climates were much warmer than today. No fossil plant remains have been discovered so far from this age in the Puna region to attest to past scenarios. Yet, we assume that the vegetation cover must have been very different from what it looks today. To test this hypothesis, we study a spore-pollen record from the mid Eocene Casa Grande Formation (Jujuy, northwestern Argentina). Although sampling is preliminary, we found ~70 morphotypes of spores, pollen grains and other palynomorphs, many of which were produced by taxa with tropical or subtropical modern distributions (e.g., Arecaceae, Ulmaceae Phyllostylon, Malvaceae Bombacoideae). Our reconstructed scenario implies the existence of a vegetated pond surrounded by trees, vines, and palms. We also report the northernmost records of a few unequivocal Gondwanan taxa (e.g., Nothofagus, Microcachrys), about 5,000 km north from their Patagonian-Antarctic hotspot. With few exceptions, the discovered taxa-both Neotropical and Gondwanan-became extinct from the region following the severe effects of the Andean uplift and the climate deterioration during the Neogene. We found no evidence for enhanced aridity nor cool conditions in the southern Central Andes at mid Eocene times. Instead, the overall assemblage represents a frost-free and humid to seasonally-dry ecosystem that prevailed near a lacustrine environment, in agreement with previous paleoenvironmental studies. Our reconstruction adds a further biotic component to the previously reported record of mammals.

Why does pollen morphology vary? Evolutionary dynamics and morphospace occupation in the largest angiosperm order (Asterales).

Morphological diversity (disparity) is a key component of biodiversity and increasingly a focus of botanical research. Despite the wide range of morphologies represented by pollen grains, to date there are few studies focused on the controls on pollen disparity and morphospace occupation, and fewer still considering these parameters in a phylogenetic framework. Here, we analyse morphospace occupation, disparity and rates of morphological evolution in Asterales pollen, in a phylogenetic context. We use a dataset comprising 113 taxa from across the Asterales phylogeny, with pollen morphology described using 28 discrete characters. The Asterales pollen morphospace is phylogenetically structured around groups of related taxa, consistent with punctuated bursts of morphological evolution at key points in the Asterales phylogeny. There is no substantial difference in disparity among these groups of taxa, despite large differences in species richness and biogeographic range. There is also mixed evidence for whole-genome duplication as a driver of Asterales pollen morphological evolution. Our results highlight the importance of evolutionary history for structuring pollen morphospace. Our study is consistent with others that have shown a decoupling of biodiversity parameters, and reinforces the need to focus on disparity as a key botanical metric in its own right.

Impact of mid Eocene greenhouse warming on America's southernmost floras.

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.

When flowering plants ruled Antarctica: evidence from Cretaceous pollen grains.

The replacement of seed-free plants and gymnosperms by flowering plants during the Cretaceous is one of the most important biotic events in the evolution of life. However, the magnitude of this global turnover remains largely unknown. Here we present sampling-standardized diversity estimates from a high resolution palynological record of the Late Cretaceous (85-66 Ma) from Antarctica, in the context of the past climatic events. Our fossil evidence reveals the occurrence of a rich Campanian flora peaking at c. 80 Ma, with angiosperms as the most diverse group of plants for the first time in Antarctica. This peak of diversity was followed by a period of a stepwise deterioration; 60% of ferns and 40% of gymnosperms became locally extinct from the early/mid-Campanian to the late Maastrichtian. Although angiosperms also faced several extinctions - 25% became extinct - they were far less affected than nonangiosperms. The onset of deterioration of the greenhouse conditions at the end of the Cretaceous - low CO2 and global cooling trends - would have led to our observed pattern of change. Overall, our study reveals the beginning of a profound floristic turnover in the highest southern latitudes that pre-dates the major extinction event of the end of the Cretaceous by 15 Myr.

Cretaceous/Paleogene floral turnover in Patagonia: drop in diversity, low extinction, and a Classopollis spike.

Nearly all data regarding land-plant turnover across the Cretaceous/Paleogene boundary come from western North America, relatively close to the Chicxulub, Mexico impact site. Here, we present a palynological analysis of a section in Patagonia that shows a marked fall in diversity and abundance of nearly all plant groups across the K/Pg interval. Minimum diversity occurs during the earliest Danian, but only a few palynomorphs show true extinctions. The low extinction rate is similar to previous observations from New Zealand. The differing responses between the Southern and Northern hemispheres could be related to the attenuation of damage with increased distance from the impact site, to hemispheric differences in extinction severity, or to both effects. Legacy effects of the terminal Cretaceous event also provide a plausible, partial explanation for the fact that Paleocene and Eocene macrofloras from Patagonia are among the most diverse known globally. Also of great interest, earliest Danian assemblages are dominated by the gymnosperm palynomorphs Classopollis of the extinct Mesozoic conifer family Cheirolepidiaceae. The expansion of Classopollis after the boundary in Patagonia is another example of typically Mesozoic plant lineages surviving into the Cenozoic in southern Gondwanan areas, and this greatly supports previous hypotheses of high latitude southern regions as biodiversity refugia during the end-Cretaceous global crisis.