Ancient DNA Clarifies the Identity and Geographic Origin of the Holotype of the Genus Ctenomys

_Ctenomys_ Blainville 1826 ranks among the top ten most diverse mammal genera in terms of species richness. However, the taxonomic history of _Ctenomys brasiliensis_ Blainville,1826, the corresponding type species, has long been obscured by a dearth of information regarding the collection data of the type material, compounded by an elusive geographic origin. Here, employing ancient DNA methodology, we sequenced the complete mitogenome of the remaining type specimen and conducted an extensive historical investigation to correlate originally described locality names with present-day locales in South America. Our analysis unequivocally confirms that the type specimen corresponds to the species currently designated as _Ctenomys minutus_ Nehring, 1887. This resolution lays to rest a century-old debate surrounding the provenance of the type specimen, rejecting prior hypotheses that placed its collection site in southeastern Brazil or Uruguay. Instead, our evidence suggests it was likely obtained from a third location in southernmost Brazil. Previous analyses overlooked this new location due to confusion surrounding geographic nomenclature and labeling errors, issues rectified by our combined mitogenomic and historical approach. Furthermore, quantitative morphological analyses boost our findings, demonstrating a closer affinity between _C. brasiliensis_ and _C. minutus_ within the same species group. Accordingly, we validate _C. brasiliensis_ and propose _C. minutus_ as its junior synonym. Our study underscores the importance of robust DNA analyses in confirming the identity and geographic origins of type specimens, especially for _Ctenomys_ species with similar phenotypes, and specimens collected centuries ago.