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Andean uplift played a fundamental role in shaping South American climate and species distribution, but the relationship between the rise of the Andes, plant composition, and local climatic evolution is poorly known. We investigated the fossil record (pollen, leaves, and wood) from the Neogene of the Central Andean Plateau and documented the earliest evidence of a puna-like ecosystem in the Pliocene and a montane ecosystem without modern analogs in the Miocene. In contrast to regional climate model simulations, our climate inferences based on fossil data suggest wetter than modern precipitation conditions during the Pliocene, when the area was near modern elevations, and even wetter conditions during the Miocene, when the cordillera was around ~1700 meters above sea level. Our empirical data highlight the importance of the plant fossil record in studying past, present, and future climates and underscore the dynamic nature of high elevation ecosystems. 

The Paleocene-Eocene boundary and the early Eocene recorded the warmest temperatures of the last 60 million years. Global estimates of sea surface temperatures and many climate models have suggested a collapse of the Neotropical forests under high tropical temperatures during the early Eocene, however, the pollen record available indicates that tropical rainforests were able to persist under the increasing temperatures. Here, we test whether increased leaf evapotranspiration and consequent thermal cooling may have provided a mechanism for tropical plants to cope with increasing temperatures and avoid thermal damage to the photosynthetic machinery. We compare leaf anatomical and geochemical data from tropical plants grown under high CO2 – high temperatures at the Smithsonian Tropical Dome Project to determine whether changes in leaf evapotranspiration can be potentially observed in fossilized leaves. Results from these experiments are then compared with late Paleocene (Cerrejón Fm., 58-60 Ma) and recently discovered early Eocene (Bogotá Fm.) leaf cuticles from Colombia, as a means to assess relative changes in leaf evapotranspiration in Neotropical rainforests during the global warming events of the early Eocene.