Eocene Rainforest conifers of the Patagonian fire lakes.

WILF, PETER; ESCAPA, IGNACIO; CÚNEO, RUBÉN

Columbus, Ohio

Congreso; Botany 2012; 2012

Caldera-lake deposits at Laguna del Hunco, ca. 52.2 Ma, and Rio Pichileufu, ca. 47.7 Ma, in Patagonia, Argentina, contain an unrivaled record of terrestrial life in South America duringthe globally warm Eocene, when the continent was only minimally separated from Antarctica and thus still linked to Australia. Along with vertebrates and insects, massive new collections have recovered more than 200 species of land plants preserved as compressions and impressions, most of them angiosperms. However, conifers are also abundant and well preserved, and they carry a great deal of biogeographic and paleoenvironmental as well as systematic information. Araucariaceae is represented by leafy branches with terminal buds, cone scales, and pollen cones of a new species of Agathis, the first from South America, as well as leafy branches and cone scales with embedded seeds of Araucaria pichileufensis Berry 1938, Section Eutacta. Cupressaceae is recorded by leafy branches attached to an immature seed cone of Papuacedrus prechilensis (Berry) Wilf et al. 2009. Podocarpaceae include short shoots of Acmopyle engelhardti (Berry) Florin 1940, leafy branches with attached seed and pollen cones of Dacrycarpus puertae Wilf 2012, leafy branches of Podocarpus andiniformis Berry 1938, and leafy branches and attached pollen cones of a new Retrophyllum species. All these lineages are found in Paleogene floras of southern Australia, in contrast to G.G. Simpson´s classic Splendid Isolation concept based on South American fossil mammals. Today, they are collectively most typical of Australasian montane rainforests with very tall canopies, to which most of them contribute. The robust Australasian rainforest connection has emerged as historic misidentifications have been corrected, some by Florin in 1940 and some in our recent work: what is now Papuacedrus was formerly linked to Austrocedrus, Dacrycarpus to Fitzroya, Acmopyle to Sequoia and Podocarpus, and Agathis to Zamia ("Z." tertiaria Engelhardt 1891). Both Acmopyle and Podocarpus preserve accessory transfusion tissue, a characteristic rainforest adaptation of these genera allowing the development of broad leaves but with high risk of sclereid collapse during droughts. Thus, in addition to improved systematic understanding and lineage-age constraints, the conifer flora greatly expands the biogeographic history of several living taxa, supporting a strong connection from Patagonia to Australia across Antarctica during the warm Eocene. Further, the fossil conifers provide abundant evidence that rainforests with tall canopies were present in Patagonia, helping to explain the extraordinary biodiversity of the fossil sites.