Co-occurrence of Prolagostomus Ameghino and Chasicomys Pascual (Caviomorpha, Rodentia) from the late Neogene of the Northwestern Argentine Puna: biostratigraphic and palaeoenvironmental implications

Abstract

Caviomorpha is a highly diversified cladeamong the Cenozoic South American mammals, notable for its extensive fossilrecord and ecological diversity. However, the evolutionary history of theCaviomorpha in the Andean and sub-Andean regions remains poorly understood. Therecent discovery of fossils from the Calahoyo locality in the PunaBiogeographic Province (northern Jujuy, Argentina) has provided insights intothis gap in our knowledge. The fossils include Chasicomys sp. (Octodontoidea) and Prolagostomus sp. (Chinchillidae) from the lower strata of aninnominate unit underlying the Tafna Formation, which represent thenorthernmost record of these taxa in Argentina. This discovery is significantin that it represents the first documented co-occurrence of these two taxa. Anabsolute zircon dating of ca. 8 Ma from a tuff located 18 m above thefossiliferous level, in conjunction with biochronologic correlations, indicatesa Late Miocene age for this level. This extends the known temporal range of Prolagostomus and enhances the significance of Chasicomys as a stratigraphic indicator for the Tortonian.The phytolith analysis indicates that the environments predominantly comprisedgrasses (Pooideae and Panicoideae) with herbaceous/woody dicotyledonouselements; with presence of palms in one area and nonphytolith elements such asdiatoms and golden algae in the other. This suggests that there were varyingmoisture levels. These findings are of crucial importance for understanding thelate Neogene evolution of the Puna ecosystem.