MUMMIFIED LEAF ASSEMBLAGE PROVIDES INSIGHT TO NEOTROPICAL FOREST ECOPHYSIOLOGY DURING THE MIDDLE MIOCENE CLIMATIC OPTIMUM

The preservation of leaf organic remains and cellular details provide a unique framework for interpreting past climates and environments based on isotopic signatures and core physiological processes that are heavily influenced by morphology. The middle Miocene climatic optimum (MMCO, 15-17 Ma) is one of the best analogues to our ongoing global warming as it occurred during the long-term global climatic cooling trend we have had for the past 20 Ma. Any paleobiological data retrieved from this time period is thus valuable for understanding current climatic perturbations. We report the recent discovery of an outstandingly preserved middle Miocene leaf assemblage from the Pedro-Miguel Formation, in the basin of the Panamá Canal. This leaf assemblage comprises at least fifteen morphotypes of (nearly) whole-leaf cuticles, some of which have been assigned to typical Neotropical families including Fabaceae, Anacardiaceae and Moraceae. We interpret that the rapid burial of the forest litter in relation to surrounding volcanic activity favored the preservation of intact cuticles and cellular details in these leaves, and provides a unique opportunity to combine leaf anatomical and biochemical data for inferring past forest ecology. The visualization of species-specific stomatal pore, epidermal and mesophyll cell size, in addition to carbon isotopic signatures can be used to infer primary leaf physiological traits such as water use efficiency, mesophyll conductance, and estimate CO₂ levels during the Middle Miocene Climatic Optimum from this Neotropical setting.