Early Eocene Palynofloral Diversity and Nothofagus Niche Modeling Across Western Gondwana

During warm intervals such as the Early Eocene, megathermal vegetation belts expanded toward higher latitudes, displacing mesothermal and microthermal biota. Here, we examine the diversity and paleoclimate of the Early Eocene Ligorio Márquez Formation (LMF) in the context of other Paleogene Patagonian palynofloras, and we model the potential distribution of Nothofagus using Early Eocene climate simulations. From 35 processed samples, 20 yielded palynomorphs and 85 morphospecies were distinguished. We hypothesize that species richness in the LMF is comparable to other Eocene microfloras, and that climate models will confirm mesothermal conditions for this formation while identifying western Gondwana as the primary region of climatic suitability for Nothofagus. Our results indicate that the LMF hosted a diverse flora under mesothermal, humid-temperate conditions (Köppen-Geiger climate Cfa, within the broader Cf no-dry-season regime). Ecological niche modeling further indicates that western Gondwana (South America, the Antarctic Peninsula, New Zealand, and Australia) provided broadly suitable climatic conditions for Nothofagus. In Experiment 1 (modern-to-Eocene transfer), Maxnet models showed high discriminatory power (AUC_test = 0.86-0.88) with low omission at P10 (OR_P10 = 0.099-0.128). In Experiment 2 (Eocene-to-Eocene calibration), performance was consistently high across GCMs (AUC_test = 0.87-0.98; OR_P10 = 0.091-0.182). However, conditions across Antarctica were likely challenging, limiting its effectiveness as a dispersal corridor during the Eocene. Finally, our results suggest that the ancient South Pacific High influenced the northern distributional limit of Nothofagus in South America.