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Rossetto-Harris, Gabriella [1], Wilf, Peter [2].

Which plants survived initial post-EECO cooling, drying, and isolation in Patagonia?

Little is known about how wet Gondwanan forests in southern South America responded to initial cooling, increased rainfall seasonality, and increasing tectonic separation from Antarctica following the Early Eocene Climatic Optimum (EECO; ~53–49 Ma). We are investigating the only well-sampled and well-dated macroflora from the early middle Eocene (ca. 47.7 Ma) of Patagonia, from Río Pichileufú (RP), Huitrera Fm., Río Negro, Argentina, using historic and recent collections. Our main point of comparison is Laguna del Hunco (LH), a well-studied, Gondwanan EECO reference flora (ca. 52.2 Ma) from the same formation and in Chubut Province. In classic work from the 1930s, E.W. Berry described over a hundred species from RP, including many putatively shared species with LH. However, most of Berry’s species have dubious identifications and have yet to be revised, which impedes accurate comparisons and estimates of diversity, turnover, and paleoenvironment. Taxa reliably identified in the RP flora include Araucariaceae (Agathis, Araucaria), Podocarpaceae (Podocarpus, Retrophyllum), Cupressaceae (Papuacedrus), Ginkgoites, Atherospermophyllum, Asteraceae, Fabaceae, Lauraceae, Myrtaceae, Proteaceae, Sapindaceae, and probable Dicksonia and Akania. Notably, most of the LH gymnosperm genera survive at RP at reduced abundances, and many Gondwanan angiosperm taxa that are abundant at LH are absent at RP, such as Gymnostoma, Ceratopetalum, and Eucalyptus. Still, much of the RP floral diversity remains in problematically assigned angiosperm leaves. To circumvent the historical misuse of botanical names, we are using a morphotype approach and comparative leaf architecture on the entire collection, including type material at the Smithsonian NMNH (Washington, D.C., USA) and recent collections at the Museo Paleontológico Bariloche (Bariloche, Argentina) and Museo Paleontológico Egidio Feruglio (Trelew, Argentina). We are comparing the new dataset for the RP flora to existing morphotype data for LH and will present a preliminary assessment of potential survivors (entities present in both floras). We validated survivorship of some taxa originally reported by Berry; however, we also identified several categories of historical problems, mostly related to Berry’s frequent use of the same names for clearly different taxa. Reevaluation of the whole RP flora, including previously unconsidered recent collections, will stabilize the morphological entities to provide a solid base for future taxonomic studies and our ongoing paleoecological investigation of the climatic and biotic evolution of the Patagonian flora during the initial post-EECO period.

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1 - Pennsylvania State University, Geosciences, 503 Deike Building, University Park, PA, 16802, USA
2 - Pennsylvania State University, Geosciences, 537 Deike Bldg., University Park, PA, 16802, United States

early Eocene climatic optimum
Río Pichileufú
Laguna del Hunco
South America
floral turnover
Leaf Architecture
leaf macrofossil

Presentation Type: Oral Paper
Session: PL1, Paleobotany: Cookson Student Presentations - Session I
Location: /
Date: Monday, July 19th, 2021
Time: 11:45 AM(EDT)
Number: PL1008
Abstract ID:241
Candidate for Awards:Isabel Cookson Award

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