First record of a lungfish (Sarcopterygii: Dipnoi) in the Upper Cretaceous of the Chubut Group, Golfo San Jorge Basin, Argentina. paleoenvironmental and paleoclimatic considerations

Abstract

Here, we describe a tooth plate (UNPSJB-PV 1047), from fluvial sandstones of the “middle section” of the Lago Colhué Huapi Formation exposed in the locality of “Playa Kruger” (Santonian?–lower Maastrichtian?), central Patagonia, Argentina. This a prearticular plate that has been assigned to the genus Metaceratodus and provisionally to the species Metaceratodus kaopen. Shared features include the presence of a lingual edge that tends to be straight and a medial edge that is slightly curved, a long first denticulation with a broad base and no deep wear facets, and an end of the first denticulation without the formation of sinuosities. However, this interpretation is not definitive given the morphological variation of tooth plates within the same species. UNPSJB-PV 1047 represents the first record of these lungfish in the Golfo San Jorge Basin, expanding the geographic distribution of this taxon in South America and contributing to interpretations of its living environment. Its presence increases biodiversity for the Lago Colhué Huapi Formation and supports interpretations of the sedimentary paleoenvironment in the “middle section” of the Lago Colhué Huapi Formation, characterized by fluvial systems that seasonally interrupted their discharge under a warm climate with dry periods, suggesting an optimal environment for the development of lungfish.