Peromyscus difficilis

From Fernández et al. (2010): "Peromyscus difficilis is endemic to Mexico and is found throughout the Sierra Madre Occidental, Sierra Madre Oriental, and adjacent mountain ranges from southwestern Chihuahua and southeastern Coahuila, south through Durango and Zacatecas. Its range continues southward from Zacatecas into parts of San Luis Potosi and mountainous regions of Guanajuato, Puebla, Hidalgo, Tlaxcala, and Veracruz, into north-central Oaxaca (Hall 1981; Hoffmeister and de la Torre 1961; Osgood 1909). Additionally, "chromosomal and molecular evidence have been used to suggest that P. difficilis and P. nasutus are sibling species (Avise et al. 1979; Bradley et al. 2007; Zimmerman et al. 1975, 1978), and these species may be sympatric in the northernmost portion of the P. difficilis distribution (Durish et al. 2004; Janecek 1990). According to Hoffmeister and de la Torre (1961), subspecies of P. difficilis average ≥219 mm in total length (range and SD were not provided by Hoffmeister and de la Torre [1961]), whereas subspecies of P. nasutus average ≤200 mm in total length. Also, the pelage of P. difficilis is generally darker (yellowish orange heavily overlaid with black) than that of P. nasutus (yellowish orange to burnt orange, only lightly overlaid with black). Length of hind foot generally is >24.5 mm in P. difficilis and <24.5 mm in P. nasutus (Hoffmeister and de la Torre 1961), and the baculum in P difficilis is generally longer (range 14.4-18.5 mm) than in P. nasutus (range 13.2-16.2 mmBurt 1960; Tamsitt 1958)."

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References

Fernández JA, García-Campusano F, Hafner MS. 2010. Peromyscus difficilis (Rodentia: Cricetidae). Mammalian Species 42(867): 220-229.