Subterranean tuco-tucos (genus Ctenomys) are a speciose group of South American hystricognath rodents, often taken as an example of explosive speciation. The 4th intron of the rhodopsin gene (567 bp) and partial sequence of the 2nd intron of the vimentin gene (403 bp) were used to assess phylogenetic relationships among 20 species of Ctenomys and 3 octodontid species. Some of the main groups of Ctenomys species previously reported in the literature (e.g., the “boliviensis” group) are confirmed, as is the lack of resolution of basal nodes. This star-like pattern of diversification of tuco-tucos was recovered with both the new nuclear dataset and an expanded mitochondrial dataset, providing further evidence that Ctenomys underwent a phase of rapid diversification early in its history.