Movement toward our current climate state began in the middle Eocene to early Oligocene interval 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. The biotic response to this event at low latitudes remains mostly unexplored. Here, we studied a recently discovered Eocene fossil macro- and palynoflora from Esmeraldas Formation (Colombia). The Esmeraldas Flora consists of more than seven hundred macrofossil specimens found in two localities, including 45 morphotypes of leaves, seeds, cuticles, fruits, and flowers and > 5000 palynomorphs, that include 210 morphospecies. The Esmeraldas Formation is dominated by meandering river floodplain deposition, and was dated, using palynology and isotopic stratigraphy, as middle to late Eocene (~47.3 to ~33.9 Ma). Quantitative paleoclimatic calculations based on leaf physiognomy and coexistence analyses indicate a warm temperature and a seasonal precipitation within the range of modern tropical dry forests. Furthermore, the floristic composition that includes the presence of macrofossils of the Pterocarpus clade (Fabaceae), and pollen records of the subfamily Bombacoideae (Malvaceae), and Euphorbiaceae, could be indicative of a tropical dry forest. The overall paleobotanical record suggests that the Esmeraldas flora represents one of the earliest records of a tropical dry forest from low latitudes.

我们目前的气候状态开始于始新世中期至渐新世早期，当时全球温度下降，第一个南极冰盖出现。这种剧烈的气候变化导致海洋和陆地生物群的全球更替。在低纬度地区对这一事件的生物反应大部分仍未得到探索。在这里，我们研究了最近从 Esmeraldas 组（哥伦比亚）发现的始新世化石大型植物群和孢粉植物群。Esmeraldas Flora 包含在两个地方发现的 700 多个大型化石标本，包括 45 种叶、种子、角质层、果实和花的形态类型以及 > 5000 种孢粉形态，其中包括 210 种形态。Esmeraldas 组以蜿蜒河流泛滥平原沉积为主，并使用孢粉学和同位素地层学确定年代，作为中至晚始新世（~47.3 至~33.9 Ma）。基于叶地貌和共存分析的定量古气候计算表明，现代热带干旱森林范围内温度较高，季节性降水。此外，植物区系组成包括存在Pterocarpus clade (Fabaceae)、Bombacoideae (Malvaceae) 和大戟科的花粉记录可能表明热带干燥森林。整体古植物学记录表明，埃斯梅拉达斯植物群代表了低纬度热带干旱森林的最早记录之一。