A South American fossil relative of Phyllocladus (Podocarpaceae), from the early Eocene of Laguna del Hunco, Patagonia, Argentina

ANDRUCHOW COLOMBO, ANA; ESCAPA, IGNACIO; WILF, PETER

Tucson

Congreso; Botany 2019; 2019

Botanical Society of America

We describe a new fossil genus and species of the conifer family Podocarpaceae from the early Eocene Laguna del Hunco site in Patagonia, Argentina, based on a single compression specimen with cuticle remains. The new taxon has spirally arranged, elongated phylloclades, delicately lobed near the apex and becoming lobed more profusely towards the base. The new genus and species shows several similarities with extant Phyllocladus (i.e., presence of phylloclades, phylloclade morphology, venation pattern), together with characters that are absent in extant Phyllocladus species but are otherwise typical of the enclosing scale-leaved clade (i.e., random stomatal orientation and arrangement). Consequently, this new genus is interpreted as a relative of Phyllocladus, possibly belonging to the stem group of the genus. This view is also supported by our phylogenetic analysis of the family Podocarpaceae that includes the new Patagonian taxon, which recovers it as sister to Phyllocladus within the here-termed phyllocladoid clade. The new fossil podocarp is the first macrofossil record of the phyllocladoid lineage in South America or anywhere in the Western Hemisphere, vastly extending its historical range and constituting an additional lineage shared between the Laguna del Hunco early Eocene rainforest and extant and extinct Australasian and SE Asian rainforests. The disappearance of the phyllocladoids from South America adds to the general extinction pattern previously described for Southern Hemisphere Podocarpaceae, interpreted to be associated with the family?s low drought tolerance in the face of climate change (i.e., aridification). The new Patagonian taxon is the oldest record known for the phyllocladoids, with a well-constrained ca. 52 Ma age, and so it represents a new reference point for temporal calibration and biogeographic inference for the evolution of conifers and Australasian rainforests.