The study of >80,000 individuals reveals that Patagonia aridlands embrace 2 marsupials and 21 rodent taxa.

Small mammal species richness in Patagonia is mainly driven by altitude.

High values of species richness in North Patagonia reflect a history of large areas free of ice and Pleistocene refugia.

Species richness mirrored the differential interplay between environmental variables and a deep glacial history.

The impoverishment of Patagonian assemblages towards high latitudes occurs by loosing taxa almost without species turnover.