CONICET | Buscador de Institutos y Recursos Humanos

Premise of research.Cenozoic macrofloras from southern South America are fundamental forunderstanding the development of extant Southern Hemisphere biotas. One siginficantassemblage is from the Paleogene Ligorio Márquez Formation (LMF), straddlingthe Chile-Argentina border, on the foot of the Andean Cordillera. Leaf-impressionfossils from the Chilean LMF have been assigned to > 50 morphotypes, interpretedas primarily representative of tropical?subtropical lineages and dominated by diverseLauraceae of extant? Neotropical genera. Here, we present new collections of ArgentineLMF mudstones that remarkably contain mummified plant fossils, including leaveswith cuticular preservation. These fossils and their unusual preservation mode complementprevious studies and provide new evidence of floristics, paleoclimate, andbiogeographic connections for Paleogene Patagonia. Methodology.Fossils were exposed by splitting blocks of mudstone or collected by flotationfrom disaggregated samples. Smaller fossils, including reproductive parts,conifer needles, and isolated cuticles were recovered from sieved slurry underbinocular microscopy. Fossils were examined under transmitted light, epifluorescence,and scanning electron microscopy. Pivotal results.The most abundant leaf species has a morphologically variable, Lauraceae-likeform but with homogeneous cuticular details that are clearly dissimilar fromthat family. Also, four-parted flower fossils attributable to the same specieshave adherent triaperturate pollen that is diagnostic for eudicots and quiteunlike that of Lauraceae. Nineteen other taxa were recognised fromcuticle-bearing leaf fossils or dispersed cuticles, including three Lauraceae, theconifers Dacrycarpus chilensis and Coronelia molinae, and a possible new speciesof Ginkgoites. A humid? mesothermpaleoclimate is inferred, and abundant fungal remains are especially indicativeof high moisture levels. Conclusions.Leaves with cuticular preservation complement and improve our understanding ofthe LMF flora, and they contribute to a greater understanding of the bioticmakeup of high southern latitudes at a time when overland dispersal waspossible between South America and Australasia. The fossils support evidencethat climates in early Paleogene Patagonia were much warmer and humid than now,with dominance of Gondwanic taxa and little conclusive evidence of taxa belongingto Neotropical and megatherm lineages.