SYSTEMATICS OF EOCENE ANGIOSPERM REPRODUCTIVE STRUCTURES FROM THE LAGUNA DEL HUNCO FLORA, NW CHUBUT PROVINCE, PATAGONIA, ARGENTINA

The early Eocene (51.9 Ma) Laguna del Hunco (LdH) flora from the Tufalitas Laguna del Hunco of northwestern Chubut Province, Argentina, is thought to be one of the most diverse Eocene fossil floras yet discovered. The fossil assemblage is preserved in tuffaceous deposits representing ancient lake sediments, and includes plants, insects, and vertebrates. Most previous research on the LdH flora has focused on leaves with the goals of documenting the diversity and paleoecology of the flora and the paleoclimate under which it existed; in contrast, little detailed study has been completed on the angiosperm reproductive organs, most of which have not undergone rigorous evaluation to place them in a systematic context. We will illustrate angiosperm reproductive structures from the LdH flora with preliminary evaluations of their systematic affinities. Assessment of overall morphological similarity suggests that the flora includes taxa with affinities to Ceratopetalum and Weinmannia (Cunoniaceae), Eucalyptus (Myrtaceae), and probably Icacinaceae, Juglandaceae, and Sapindaceae. We plan to perform phylogenetic analyses for each fossil taxon to place it in the most precise evolutionary context possible. As an example, we will show results of phylogenetic analyses of fossils assigned to Eucalyptus. These fossils show morphological characteristics—particularly, presence of a calycine operculum scar in bud—that provide evidence for a relationship with the species-rich extant taxon Eucalyptus subgenus Symphyomyrtus of Australia, New Guinea, and adjacent islands, thus reinforcing an emerging pattern that links LdH taxa such as the previously published Akania (Akaniaceae), Gymnostoma (Casuarinaceae), and Papuacedrus (Cupressaceae), and the tentatively identified Ceratopetalum to the extant endemic flora of Australasia (Wilf et al., this volume). Other putative living relatives of LdH fossils, however, such as Weinmannia, have more complex distributions. Thus, phylogenetic assessment is critical to determining whether these taxa fit the pattern of evolutionary relationship to extant Australasian endemics shown by some components of the LdH flora.