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Chinchilla rats (family Abrocomidae) are hystricomorph rodents primarily inhabiting the central Andes in South America with 8 species in the genus Abrocoma and 2 in Cuscomys. The systematics of this family—relying only on morphological differences—has faced several controversies, particularly in arid-adapted species of Abrocoma (the A. cinerea species complex, or ACC). By using partial DNA sequences of 1 mitochondrial (Cytochrome b) and 2 nuclear genes (GHR and RAG1), we: (i) inferred phylogenetic relationships between 5 species of Abrocoma and 1 of Cuscomys ; (ii) performed molecular species-delimitation analyses in 4 species of the ACC (A. cinerea , A. famatina , A. schistacea , and A. uspallata); and (iii) estimated divergence times using stratigraphic ages of extinct taxa. Our phylogenetic analyses recovered 3 main clades: A. bennettii (basal); C. ashaninka ; and the ACC. Striking differences in habitat use, morphology, and genetics suggest that each of these main clades might represent a distinct genus. In species-delimitation analyses in the ACC, only 2 species were recognized, and we thus suggest the synonymy of A. famatina with A. cinerea and of A. uspallata with A. schistacea. The origin of extant abrocomids was estimated at the late Miocene (~5.6 million years ago, Ma) with the subsequent origin of arboreal species during the early Pliocene (~4.3 Ma) and the ACC during the late Pliocene (~3.3 Ma). We hypothesize that topographic uplift of the central Andes and associated climatic and ecological changes were the main drivers of diversification in this family. [ABSTRACT FROM AUTHOR]