Late Miocene mammals from the Calchaquí Valley (Palo Pintado formation, northwestern Argentina) : biogeographic and paleoenvironmental implications for the southern central Andes

Abstract

With noteworthy outcrops in the Angastaco Basin (Salta Province), the Palo Pintado Formation is perhaps one of the most intensely studied late Miocene stratigraphical unit of northwestern Argentina from geological, paleoecological, and paleobotanical approaches. In contrast, the mammals from this unit are scarcely known, most of them lacking a precise stratigraphical and geochronological adjustment. In this contribution, we report new caviomorph rodents from the Palo Pintado Fm, exposed at Calchaquí Valley (Eastern Cordillera, Angastaco Basin). The stratigraphical and geochronological control of the new specimens indicate a time window ranging from ~9.3 Ma to ~6.1 Ma. The first records of brachydont mammals of the Palo Pintado Fm, represented by the caviomorph Erethizontidae (Erethizontidae sp. nov. cf. Microsteiromys sp.) and Echimyidae (cf. “Eumysops” parodii, and cf. Thrichomys sp.), are described. Dinomyidae (cf. Ferigolomys sp.), small Caviidae (gen. and sp. indet. A and B), and the abrocomid Protabrocoma paranensis are also identified. Caviomorphs from the Palo Pintado Fm (containing the oldest and more recent taxa of different Neotropical linages) allow us to suggest Angastaco Basin as “museum” and “cradle” of biodiversity during the Tortonian and Messinian ages. Our análisis indicates that the late Miocene mammals of the Palo Pintado Fm are compatible with the occurrence of forested environments developed under humid and warm conditions, in agreement with independent paleoenvironmental and paleoclimatic proxies. A close biogeographic relationship between the area of the Calchaquí Valley, the Brazilian Acre, and the Argentinian Mesopotamia during the late Miocene is also suggested.