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The Reithrodontomys tenuirostris species group is considered “the most specialized” within the genus Reithrodontomys from morphological and ecological perspectives. Previous studies based on molecular data recommended changes in the taxonomy of the group. In particular, R. microdon has been the most taxonomically questioned, with the suggestion that it constitutes a complex of cryptic species. We analyzed the phylogenetic relationships of the R. tenuirostris species group using DNA sequences from the mitochondrial Cytochrome b gene and Intron 7 of the nuclear beta fibrinogen gene. In addition, divergence times were estimated, and possible new taxa delimited with three widely used species delimitation methods. Finally, possible connectivity routes based on shared haplotypes were tested among the R. microdon populations. All species were recovered as monophyletic with the exception of R. microdon, whose individuals were grouped into four different haplogroups, one of which included specimens of R. bakeri. Diversification within the R. tenuirostris species group began about 3 Ma, in the Pleistocene. The bGMYC and STACEY delimitation methods were congruent with each other, delimiting at the species-level each haplogroup within R. microdon, while the mPTP suggested a greater number of species. Moreover, none of the haplogroups showed potential connectivity routes between them, evidencing lack of gene flow. Our results suggest the existence of a higher number of species in the R. tenuirostris group, because we show that there are four species within what is currently recognized as R. microdon.

Reithrodontomys albilabris Merriam, 1901 Type locality. “ Cerro San Felipe, Oaxaca, Mexico (altitude 10,000 ft.)”. Synonym. Reithrodontomys microdon albilabris Merriam, 1901:549. Type locality: see above. Distribution. Oaxacan Highlands. Known range (in addition to type locality) included Cerro Zempoaltepec, Vista Hermosa, Llano de las Flores, Cerro Pelón (Hall 1981), and Ixtepeji (this study), Mexico. Remarks. Reithrodontomys albilabris comprises the specimens representing haplogroup IV, with the exception of the individual CMC 1627. Information on type material and morphological characteristics is available in Merriam (1901) and Howell (1914)., Published as part of Martínez-Borrego, Daily, Arellano, Elizabeth, González-Cózatl, Francisco X, Castro-Arellano, Ivan, León-Paniagua, Livia & Rogers, Duke S, 2022, Molecular systematics of the Reithrodontomys tenuirostris group (Rodentia: Cricetidae) highlighting the Reithrodontomys microdon species complex, pp. 29-44 in Journal of Mammalogy 103 (1) on page 41, DOI: 10.1093/jmammal/gyab133, http://zenodo.org/record/7832553, {"references":["Merriam C. H. 1901. Descriptions of 23 new harvest mice (genus Reithrodontomys). Proceedings of the Washington Academy of Sciences 3: 547 - 558.","Hall E. R. 1981. The mammals of North America. 2 nd ed. Vol. 2. Hoboken, New Jersey: Wiley.","Howell A. H. 1914. Revision of the American harvest mice (Genus Reithrodontomys). North American Fauna 36: 1 - 97."]}

Reithrodontomys microdon Merriam, 1901 Type locality. “ Todos Santos, Guatemala (altitude 10,000 ft.)”. Synonym. Reithrodontomys microdon microdon Merriam, 1901:548. Type locality: see above. Distribution. Highlands of Guatemala (Howell 1914), and the extreme southern portion of Mexico (Hooper 1952). This species is distributed from the highlands of central and southern Chiapas in Mexico to the southwestern region of Guatemala. Remarks. For additional information on type material, cranial measurements, morphological characteristics, habitat, and comparisons with other species of the subgenus Aporodon, see Hooper (1952:170)., Published as part of Martínez-Borrego, Daily, Arellano, Elizabeth, González-Cózatl, Francisco X, Castro-Arellano, Ivan, León-Paniagua, Livia & Rogers, Duke S, 2022, Molecular systematics of the Reithrodontomys tenuirostris group (Rodentia: Cricetidae) highlighting the Reithrodontomys microdon species complex, pp. 29-44 in Journal of Mammalogy 103 (1) on page 41, DOI: 10.1093/jmammal/gyab133, http://zenodo.org/record/7832553, {"references":["Merriam C. H. 1901. Descriptions of 23 new harvest mice (genus Reithrodontomys). Proceedings of the Washington Academy of Sciences 3: 547 - 558.","Howell A. H. 1914. Revision of the American harvest mice (Genus Reithrodontomys). North American Fauna 36: 1 - 97.","Hooper E. T. 1952. A systematic review of harvest mice (Genus Reithrodontomys) of Latin America. Miscellaneous Publications of the Museum of Zoology, University of Michigan 77: 1 - 255."]}