ABSTRACT Here we describe two new caviomorphs from the early Oligocene Tinguiririca Fauna of the Andean Main Range of central Chile, representing the most ancient rodents known from the mid to high latitudes of South America, and the second-oldest securely dated rodents from the continent. These two new taxa are each documented by single partial mandibles bearing largely complete dentitions. Representing two new taxa, Andemys termasi gen. et sp. nov., and Eoviscaccia frassinettii, sp. nov., these caviomorphs are informally referred to the pan-Dasy-proctidae and pan-Chinchillidae, respectively. These taxa, together with recent findings in Peru, confirm that caviomorphs were well diversified prior to the Deseadan SALMA, that they likely originated during the middle to late Eocene, but that they did not spread from the tropics until some time after the Mustersan—a well-sampled interval from which rodents are unknown in higher latitudes. Additionally, in documenting the earliest occurrence of hypsodonty among...