LEGUME FOSSILS FROM THE EARLY EOCENE LAGUNA DEL HUNCO PALEOFLORA, CHUBUT, PATAGONIA, ARGENTINA

The Early Eocene Laguna del Hunco flora from Chubut, Patagonia, Argentina is one of the world's most diverse Tertiary assemblages of angiosperms. This paleoflora was deposited in tuffaceous mudstones and sandstones of the Tufolitas Laguna del Hunco, which are described as a lacustrine unit of the middle Chubut River volcanic-pyroclastic complex. The flora is even more interesting because its paleofloristic association is composed of tropical elements (i.e. Akania, and Gymnostoma) restricted today to temperate and tropical Australasia; other elements (i.e. Anacardiaceae and Melastomataceae) that are considered to be modern pantropical, and elements of austral origin (i.e. Proteaceae and Podocarpaceae). In this contribution, we describe fossil taxa with affinities to Leguminosae, a family of cosmopolitan distribution. Leguminosae or Fabaceae comprises more than 700 genera and 17000 species belonging to three subfamilies (Papilionoideae, Caesalpinioideae and Mimosoideae) The morphotypes presented here are based on compressions of leaves and a single fruit, and correspond to members of the subfamilies Papilionoideae and Caesalpinioideae.The subfamily Papilionoideae is represented by fossils assignable to the tribes Swarztieae (Zollernia), Brongniartieae (Hovea), Phaseoleae (Rhynchosia), and Desmodieae (Desmodium), while the subfamily Caesalpinioideae is confirmed by the presence of the tribes Detarieae (Hymenaea), Cercideae (Cercis), and Caesalpinieae (Sclerolobium). The tribe Caesalpinieae is also represented by a fossil fruit probably belonging to the genus Caesalpinia. These fossils allow confirmation of the presence of Leguminosae in Patagonia at least since the early Eocene. The presence of two of the three subfamilies by the early Eocene also suggest that the legumes probably already diversified at the subfamilial level in Argentina by the Paleogene. Although the center of origin for the family is uncertain, the presence of these taxa further highlights the diversity and varied biogeographic relationships of the family, adding information for future discussions of its hypothetical origin.