New vertebrates from the Late Miocene of Entre Ríos Province, Argentina: diversity, age, and paleoenvironment

New remains of fossil vertebrates recovered from two localities in Entre Ríos Province, Argentina, are studied. The specimens were found at Toma Vieja and Arroyo Chapetón localities, where the fossiliferous Lower Member (“Mesopotamiense”, Late Miocene) of Ituzaingó Formation (Late Miocene–Pliocene) crops out. The new findings contribute to the high diversity of fossil vertebrates largely known for this unit. The specimens correspond to Perciformes indet. and Pimelodidae indet. (Pisces), Macranhinga paranensis (Aves), Scirrotherium carinatum, Brachytherium cuspidatum, Proterotheriinae indet., Hydrochoerinae indet., and cf. Prodolichotis (Mammalia). Considering the relationship between the fauna present in this unit and that from other mammal-bearing Neogene units (e.g., Arroyo Chasicó, Andalhuala, Cerro Azul, and Monte Hermoso formations), the “Mesopotamiense” is a faunal combination of Chasicoan and Huayquerian taxa deposited during the end of the Tortonian or the early Messinian. From a paleoenvironmental point of view, the “Mesopotamiense” faunal assemblage is indicative of a mosaic of ecological niches developed under tropical–subtropical conditions. •Fossil vertebrates from Entre Ríos Province (Argentina) are described.•Fossils come from of the Lower Member (“Mesopotamiense”) of Ituzaingó Formation.•The “Mesopotamiense” is represented by a mixture of Chasicoan and Huayquerian faunas.•The “Mesopotamiense” was deposited during the end of the Tortonian or the early Messinian.•This faunal assemblage is indicative of a mosaic of ecological niches developed under tropical–subtropical conditions.