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A major reorganization of Patagonian ecosystems occurred when permanent ice sheets appeared in Antarctica and the Andean Range uplifted in southern South America. Rich plant communities dominated by Gondwanan trees and other species with tropical modern distribution vanished and those with cool and arid distributions rose to prominence. Rather than a single event, this landscape-level floristic replacement may have occurred as pulses following the paleoclimatic dynamism of the Coolhouse state (~34–4 Ma). However, the associated shifts in diversity and in climatically-key sensitive plant species have never been studied in detail so far. Here, we estimated richness using robust (non-parametric) methods and selected climatically-sensitive species to trace back past floristic trends in the high southern latitudes during the Coolhouse state. We used a high resolution palynological record from well-constrained Patagonian sediments from the Early Oligocene to the Late Miocene (~34–10 Ma), spanning most of the Coolhouse state. Our fossil data reveal the presence of five major floristic phases, closely linked with global climate states and regional orographic events. We found that diversity rises during global warming periods (↑100% at the Late Oligocene Warming Event or LOWE and ↑50% at the Miocene Climatic Optimum or MCO) and drops during glaciation periods (↓60% at Oi-1 (earliest Oligocene), ↓50% at Mi-1 (earliest Miocene) and ↓35% at Mi-3 (Middle Miocene) glaciation events) or intense tectonism (↓60% after the Andean uplift), relative to background levels. The representation of warm-demanding taxa peaked during LOWE and MCO, while arid-adapted taxa rose briefly during the MCO and took over following the major surface uplift of the southern Andes by 15–14 Ma. Humid-demanding species (e.g., tree-ferns) showed a general decreasing trend in abundance from their climax at 34 Ma to their minimum occurrence at 10 Ma. Our study reveals the potential of using robust statistical diversity methods in unraveling the relationship between past floras and climatic-orogenic forcing during the Coolhouse state. • Plant richness during the MCO is remarkably higher than background levels. • Plant richness falls during glaciation events of the coolhouse state. • Fluctuations in plant richness and diagnostic key-sensitive climatic taxa closely follow the most important climatic trends. [ABSTRACT FROM AUTHOR]

A major climate shift took place about 40 Myr ago-the Middle Eocene Climatic Optimum or MECO-triggered by a significant rise of atmospheric CO 2 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 CO 2 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.

Background and Aims: Morphological, molecular and biogeographical information bearing on early evolution of the sunflower alliance of families suggests that the clade containing the extant daisy family (Asteraceae) differentiated in South America during the Eocene, although palaeontological studies on this continent failed to reveal conclusive support for this hypothesis. Here we describe in detail Raiguenrayun cura gen. & sp. nov., an exceptionally well preserved capitulescence of Asteraceae recovered from Eocene deposits of northwestern Patagonia, Argentina., Methods: The fossil was collected from the 47·5 million-year-old Huitrera Formation at the Estancia Don Hipólito locality, Río Negro Province, Argentina., Key Results: The arrangement of the capitula in a cymose capitulescence, the many-flowered capitula with multiseriate-imbricate involucral bracts and the pappus-like structures indicate a close morphological relationship with Asteraceae. Raiguenrayun cura and the associated pollen Mutisiapollis telleriae do not match exactly any living member of the family, and clearly represent extinct taxa. They share a mosaic of morphological features today recognized in taxa phylogenetically close to the root of Asteraceae, such as Stifftieae, Wunderlichioideae and Gochnatieae (Mutisioideae sensu lato) and Dicomeae and Oldenburgieae (Carduoideae), today endemic to or mainly distributed in South America and Africa, respectively., Conclusions: This is the first fossil genus of Asteraceae based on an outstandingly preserved capitulescence that might represent the ancestor of Mutisioideae-Carduoideae. It might have evolved in southern South America some time during the early Palaeogene and subsequently entered Africa, before the biogeographical isolation of these continents became much more pronounced. The new fossil represents the first reliable point for calibration, favouring an earlier date to the split between Barnadesioideae and the rest of Asteraceae than previously thought, which can be traced back at least 47·5 million years. This is the oldest well dated member of Asteraceae and perhaps the earliest indirect evidence for bird pollination in the family.