Morphologic characterization of Peromyscus schmidlyi (Rodentia: Cricetidae), an endemic of the Sierra Madre Occidental, Mexico

Based on examination of 705 museum specimens, including the holotype and individuals identified using molecular attributes, we characterized Schmidly's deer mouse (Peromyscus schmidlyi) using a set of morphometric and morphological characteristics. Discriminant function analysis was performed on 14 cranial attributes to find those most useful to separate species. Factorial analysis of variance and multivariate analysis of variance were used to test for significant differences due to species, sex, age, and geographic location. We compared and contrasted P. schmidlyi with P. boylii rowleyi and P. spicilegus, morphologically similar and partially sympatric species, and reevaluated the distribution of the 3 species in the Sierra Madre Occidental (SMO) of Mexico. P. schmidlyi is a medium-sized Peromyscus distinguishable by a set of characters including overall size intermediate between P. spicilegus and P. boylii rowleyi, relatively wider braincase and zygoma, hourglass-shaped interorbital constriction, large auditory bullae, and strongly bicolored, tufted tail. Morphometric characterization is possible only when age and geographic location are taken into consideration. Several specimens previously identified as P. boylii rowleyi were reidentified as P. schmidlyi. Records available showed that P. schmidlyi is distributed in forested highlands of the SMO, from northern Chihuahua to northern Jalisco, between 1,550 (on the western versant) and 3,000 m of elevation. The species is sympatric with P. boylii rowleyi between 2,100 and 2,400 m along the eastern versant of the SMO and with P. spicilegus along a narrower band (1,550-2,000 m) on the steeper western slope. Distribution of these species closely reflects the most recent ecological regionalization of the SMO.