Nothofagus fruits from the mid-Campanian of the Antarctic Peninsula

BANDEIRA,, E.V.; IGLESIAS, A.; ATKINSON, B.; PASSALIA, M.G.; PICCA, P.; SMITH, S.

Conferencia; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2023

The Campanian-aged deposits from the Beta Member of the Santa Marta Formation (James Ross Island, Antarctic Peninsula) contains an extensive assemblage of plants that are exceptionally preserved within carbonate concretions. Permineralized vegetative and reproductive organs, including wood, leafy branches, leaves and petioles, fruits, and seeds, are studied via serial acetate peels, light microscopy, and x-ray tomography. Thus far a striking diversity of plants have been identified from this deposit including: callitroid Cupressaceae, Araucariaceae, Podocarpaceae, cycads, diverse angiosperms (including Sarcandra-like Chloranthaceae, Cunoniaceae, Lauraceae, and Nothofagaceae), ferns (including Pteridaceae, Gleicheniaceae, and ?Schizaeaceae) and bryophytes (acrocarpous mosses). Two winged fruit types are identified as belonging to the genus Nothofagus. These fruits have two or three fused carpels and three clearly differentiated fruit layers: an outermost sclereid layer with vascular bundles, a middle zone with interlocking fibrous cells, and a thin endocarp with glabrous lining. Each locule contains two ovules with axile placentation. All these features are diagnostic of Nothofagus representing the oldest record for the genus, besides coeval associated ancient-form-like pollen grains assigned to the family Nothofagaceae. Furthermore, the studied fossil fruits are the oldest macrofossil record of reproductive structures for this family. Nothofagus today constitutes dense forests distributed around the South Pacific, representing the dominant trees in the Antarctic and sub-Antarctic forests since the Paleogene. The Santa Marta Formation record contributes to the understanding of how Nothofagaceae evolved during the Late Cretaceous in these highest latitude environments. Our findings indicate that three-flowered cupules (with a middle bicarpellate flower)