PALEOCLIMATIC AND PALEOECOLOGICAL RECONSTRUCTION OF A MIDDLE TO LATE EOCENE SOUTH AMERICAN SEASONALLY DRY TROPICAL FOREST

An important step towards our current climate state occurred throughout the middle Eocene to early Oligocene when the global temperature cooled, and the first Antarctic ice sheet appeared. This dramatic climate change caused a significant global turnover in both marine and terrestrial biotas. Evidence from tropical regions is, however, still needed to study the biotic response of this climatic change at low latitudes. Here, we studied a recently discovered Eocene fossil macro- and microflora assemblage from the Esmeraldas Formation (Colombia). This fossil flora provides a first glance to document the influence of this global climatic change in terrestrial tropical regions. The Esmeraldas Flora has been collected from two localities and has more than seven hundred specimens that include compressions and impressions of leaves mostly, but also seeds, cuticles, fruits and seldom flowers. Detailed stratigraphic data shows that the floristic assemblage was deposited on the floodplains of braided and meandering rivers. Furthermore, chemostratigraphic and palynological analyses indicated that the Esmeraldas Flora age is middle to late Eocene. A total of 35 leaf morphotypes were described from both localities. Quantitative paleoclimatic analyses based on leaf margin and leaf area examination from the Esmeraldas fossil assemblage suggest drier conditions during deposition compared to the present climatic state. Furthermore, morphologic analyses of fertile material and their comparisons with extant taxa suggest the presence of families like Fabaceae, Menispermaceae, Passifloraceae, Salviniaceae, Solanaceae, and possibly Cyperaceae. The evidence presented here suggests that the Esmeraldas Flora could represent the earliest record of a seasonally dry forest in tropical regions.