Until the discovery of the genus Punahyrax (Geste Formation) in different localities of Catamarca and Salta provinces, “archaeohyracids” were unknown in northwestern Argentina. Here we analyze the record of these notoungulates in the region through specimens known for the Geste Formation and new remains recovered from the lower levels of the Quebrada de Los Colorados Formation, assessing their diversity and significance in the context of the pre-Deseadan radiation of Typotheria. We identify three “archaeohyracid” morphotypes for Barrancan levels and four for Mustersan levels in northwestern Argentina, implying the possible presence of as much as seven “archaeohyracid” taxa in the region for the last third of the Eocene, and illustrating a striking diversity, especially considering the scarce pre-Tinguirirican record known until now. These new records underline the faunal differences of the Geste and Quebrada de los Colorados formations regarding the highly fossiliferous Lower and Upper Lumbrera formations. In this sense, although the existence of a sample bias should not be completely dismissed, the possibility of important biogeographic barriers acting in the area by the late middle Eocene needs to be analyzed with independent evidence. The record of Pseudhyrax eutrachytheroides in northwestern Argentina represents the first notoungulate taxon common between this region and typical Patagonian localities and represents a useful and presumably reliable new basis for the assignment of a Mustersan age for the middle section of the Geste Formation.