An ichthyological assemblage from the Early Holocene in the distal Paraná River basin (Entre Ríos, Argentina): systematics, taphonomy, and palaeoenvironmental reconstructions

The southern Entre Ríos province (eastern Argentina) is an area yielding Quaternary palaeontological deposits with a tropical and subtropical fauna. Here, we analysed freshwater fish remains recovered from Early Holocene palaeontological sites in southwestern Entre Ríos province, Argentina. These sites outcrop along the banks of Doll creek, in the distal part of the Paraná Basin. At least 12 taxa were identified, belonging to the orders Characiformes, Cichliformes, Siluriformes, Cyprinodontiformes, and Synbranchiformes. This freshwater fossil fish assemblage represents the most taxonomically diverse known for the Quaternary of Argentina in a non-archaeological context. The ecological requirements of the recovered taxa, combined with sedimentological, stratigraphic, and taphonomical analyses, suggest the presence of lentic and/or ephemeral watercourses, such as lagoons and slow-flowing streams with abundant aquatic vegetation. Our results indicate that, during the Early Holocene, the southwestern Entre Ríos province experienced predominantly interglacial conditions, characterised by a temperate-warm climate with water availability (humid conditions). The interaction between these environmental conditions and aquatic organisms suggests a dynamic and diverse ecosystem, favourable for the development of such assemblages.