Marine vertebrate assemblages in the southwest Atlantic during the Miocene

Abstract

Two biogeographical units are generally recognized in the present shelf area of Argentina: the Magellanian andArgentinian Provinces. The two provinces differ in their fossil record. The evolution of these provinces has beencharacterized by migrations, extinctions, pseudoextinctions and, perhaps, even speciation events. Marine vertebrateassemblages with some similarities to the Argentinian fauna were already present in the Miocene, whereasno associations similar to those of the Magellanian fauna have been found in South America before the Pleistocene.Two successive major marine transgressions flooded northern Patagonia during the Miocene: the ‘Patagoniense’(Early Miocene) and the ‘Entrerriense’ (Middle to Late Miocene). We analyse three rich fossil assemblages thatwere formed during these transgressions. The absence of Magellanian Miocene vertebrate assemblages is consistentwith the hypothesis of a more southern distribution of the cold-temperate fauna at that time. In Patagonia,as in other regions, an increased number of living groups appeared from the Lower to Upper Miocene. The LateMiocene aquatic mammals had a modern aspect, and some of the fish species are still living in the South AtlanticOcean. In this contribution, we stress that warm-temperate fishes and a high diversity of penguins are foundtogether at the base of the Gaiman Formation. We hypothesize that penguins were adapted to live in warmerwaters than those of the latest Cenozoic and the Recent. Finally, we recall that many taxa became extirpatedbecause of the global temperature drops of the late Cenozoic.