. Palm fruits from the Chichinales Formation (Upper Oligocene-Middle Miocene), northern Patagonia, Argentina

MUCI, A.L.; PASSALIA, M.G.; IGLESIAS, A.

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

Palms (Arecaceae) has the broadest stratigraphically and geographically fossil record among monocots. The oldest global fossils of palms are late Barremian-Albian (Lower Cretaceous) pollen grains from the Austral Basin, Patagonia. For the Late Cretaceous, the finding of macrofossils as permineralized stipes and leaf compressions are frequent. On the contrary, fossil palm fruits are very scarce in the literature, being a single occurrence for Patagonia (Paleocene in the Chubut Province) the sole published fossil record for southern South America. In this communication, we present the preliminary study of palm fruits from the Chichinales Formation (Upper Oligocene–Middle Miocene) exposed in the Paso Córdoba area, Río Negro Province. The fossils consist of ca. 150 permineralized and natural-cast fruits, which were found as isolated specimens or included in a carpoflora (natural fruit concentration) in a fine-grained siliceous cemented sandstone (chert). The external morphology and inner anatomical features of the fossil fruits, including the three fused endocarp and presence of three germination pores, consents a clear affinity within the Tribe Cocoseae (Subfamily Arecoideae). Furthermore, the germination pores in basal position allows its assignment of the Subtribe Attaleinae. This record corresponds to the only fossil fruits of this important group of palm trees for South America; and reaffirms the presence of the Cocoseae Tribe in Patagonia, based on previous fossil stipes. Previous lithofacial analyses suggest a low sinuosity fluvial environment for the Chichinales Formation, that, together with the fossil fauna (mammals, birds and reptiles), point to subtropical continental climatic conditions. Other plant fossils from this unit include fragments of permineralized logs (Nothofagoxylon menendezii), as well as non-studied leaves, fruits and seeds; being the present work the first of them. The presence of this palm group in the Chichinales Formation is consistent with the previous paleoclimatic interpretation; furthermore, it association with the northernmost Patagonian record of Nothogafaceae would indicate climatic conditions similar to those currently developed in mediterranean climates. The studied materials are housed at the MPCN Collection (General Roca, Río Negro) and MAPBAR Collection (Bariloche, Río Negro).