This species was originally described as a
subspecies of the
Mexican pygmy mouse (
B. musculus). It was considered a subspecies of
B. musculus until 2021, when it was determined that most populations formerly considered part of
B. musculus should instead belong to
B. brunneus. The
Trans-Mexican Volcanic Belt and the
Balsas River, form a barrier between
B. musculus to the west and
B. brunneus to the east. This species, as well as
B. musculus, are likely more
basal within
Baiomys than the
northern pygmy mouse, since they moreso resemble fossil species. There are seven recognized
subspecies: •
B. b. brunneus J. A. Allen & F. M. Chapman, 1897 - native to central
Veracruz, eastern
Puebla, and a small part of northernmost
Oaxaca •
B. b. grisescens E. A. Goldman, 1932 - native to southern Guatemala, northern El Salvador, and southwestern Honduras •
B. b. handleyi Packard, 1958 - only known from
Sacapulas in central Guatemala •
B. b. infernatis Hooper, 1952 - only known from southern
Puebla and northwestern Oaxaca •
B. b. nigrescens Osgood, 1904 - native to southern Honduras, most of El Salvador, southern Guatemala, and most of the Mexican state of
Chiapas •
B. b. pallidus Russell, 1952 - native to southern and western Oaxaca, most of
Guerrero, southern
Estado de Mexico,
Morelos, southern
Mexico City and southwestern Puebla •
B. b. pullus Packard, 1958 - native to southernmost Honduras and northwestern Nicaragua == Description ==