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 clade among the Cenozoic South American mammals, notable for its extensive fossil record and ecological diversity. However, the evolutionary history of the Caviomorpha in the Andean and sub-Andean regions remains poorly understood. The recent discovery of fossils from the Calahoyo locality in the Puna Biogeographic Province (northern Jujuy, Argentina) has provided insights into this gap in our knowledge. The fossils include Chasicomys sp. (Octodontoidea) and Prolagostomus sp. (Chinchillidae) from the lower strata of an innominate unit underlying the Tafna Formation, which represent the northernmost record of these taxa in Argentina. This discovery is significant in that it represents the first documented co-occurrence of these two taxa. An absolute zircon dating of ca. 8 Ma from a tuff located 18 m above the fossiliferous level, in conjunction with biochronologic correlations, indicates a 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 comprised grasses (Pooideae and Panicoideae) with herbaceous/woody dicotyledonous elements; with presence of palms in one area and non-phytolith elements such as diatoms and golden algae in the other. This suggests that there were varying moisture levels. These findings are of crucial importance for understanding the late Neogene evolution of the Puna ecosystem.