New caviomorph rodents from the late Oligocene of Salla, Bolivia: taxonomic, chronological, and biogeographic implications for the Deseadan faunas of South America

Abstract

Caviomorph rodents have been an important component of South American mammal faunas at least since the Oligocene. Those from the Deseadan South American Land Mammal Age (SALMA; late Oligocene) have been exhaustively studied because they are considered key to understanding the evolution of South American rodents. Deseadan faunas are widely distributed from northern Peru to central Patagonia, with those from Salla (Bolivia) and Cabeza Blanca (Argentinean Patagonia) being the most diverse. Recent studies of Deseadan rodents at some localities in high (Cabeza Blanca, Punta Nava, Scarritt Pocket) and low (Contamana) latitudes revealed greater taxonomic diversity. However, at middle latitudes, Salla has not received the same attention, despite being exceptional in terms of the abundance and high-quality preservation of specimens. The aim of this work is to report new caviomorph rodents from Salla, and to discuss their systematic and palaeobiogeographical implications in the context of the South American Deseadan caviomorph assemblages. We describe two new genera (†Lapazomys gen. nov. and †Cholamys gen. nov.) and five new species (†Migraveramus lavocati sp. nov., †Sallamys woodi sp. nov., †Lapazomys hartenbergeri sp. nov., †Protosteiromys pattersoni sp. nov. and †Cholamys tetralophodonta sp. nov.). These include the first erethizontids and the oldest Cavioidea sensu stricto for middle and low latitudes. The increase in the number of species corroborates the existence of an important rodent diversification already evidenced in the late early/early late Oligocene. In addition, the new rodents lessen the degree of endemism of the Salla rodent fauna proposed in previous papers. We interpret that the differences among Deseadan assemblages from low, middle and high latitudes are due essentially to climatic, historical and local environmental conditions, whereas diachronism seems less important in the modelling of faunas.