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 and Argentinian Provinces. The two provinces differ in their fossil record. The evolution of these provinces has been characterized by migrations, extinctions, pseudoextinctions and, perhaps, even speciation events. Marine vertebrate assemblages with some similarities to the Argentinian fauna were already present in the Miocene, whereas no 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 that were formed during these transgressions. The absence of Magellanian Miocene vertebrate assemblages is consistent with 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 Late Miocene aquatic mammals had a modern aspect, and some of the fish species are still living in the South Atlantic Ocean. In this contribution, we stress that warm‐temperate fishes and a high diversity of penguins are found together at the base of the Gaiman Formation. We hypothesize that penguins were adapted to live in warmer waters than those of the latest Cenozoic and the Recent. Finally, we recall that many taxa became extirpated because of the global temperature drops of the late Cenozoic. However, some fishes and pinnipeds which were extirpated only in the Atlantic Ocean are discussed here. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 423–440. Actualmente se reconocen dos provincias biogeográficas en la plataforma marina argentina actual: la Magallánica y la Argentina. Las dos unidades difieren en su registro fósil. Se sugiere aquí que la evolución de las provincias fue compleja y caracterizada por migraciones, eventos de especiación, extinciones, pseudoextinciones. Durante el Mioceno ya había asociaciones de vertebrados marinos con similitudes taxonómicas con los de la Provincia Argentina pero no se detectaron hasta ahora asociaciones fósiles similares a las de la Magallánica hasta el Pleistoceno. Aquí describimos tres ricas asociaciones faunísticas marinas del Mioceno que se depositaron durante dos grandes transgresiones atlánticas: el ‘Patagoniense’ (Mioceno Temprano) y el ‘Entrerriense’ (Mioceno Medio a Tardío). La ausencia de asociaciones de tipo magallánicas en el Mioceno confirma la hipótesis de que la fauna templado‐fría se distribuía más al sur en ese tiempo. En Patagonia, tal como en otras áreas, se registra un número mayor de formas actuales desde el Mioceno Temprano al Tardío. Los mamíferos acuáticos del Mioceno Tardío tenían un aspecto moderno; incluso alguna de las especies de peces perdura en la actualidad. Asimismo, en este trabajo llamamos la atención sobr...

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