Sigmodon ochrognathus

Yellow-nosed Cotton Rat
(*Sigmodon ochrognathus*)
Yellow-nosed Cotton Rat (Sigmodon ochrognathus)
Range
Taxonomic classification
Order:	Rodentia
Suborder:	Supramyomorpha
Infraorder:	Myomorphi
Superfamily:	Muroidea
Family:	Cricetidae
Subfamily:	Sigmodontinae
Tribe:	Sigmodontini
Genus:	Sigmodon
Binomial details
	Sigmodon ochrognathus V. O. Bailey, 1902
Other resources
	Full taxonomic details at MDD

The Yellow-nosed Cotton Rat (Sigmodon ochrognathus) is a cotton rat found in the desert mountains of southeastern Arizona, southwestern New Mexico, west Texas, and north-central Mexico.

Description

From Hoffmesiter (1986): "A Sigmodon with a conspicuous "yellow" nose which is actually a nose ring of orangeish or ochraceous; eye ring of similar color; small to medium size; hind foot 30 mm or shorter; underparts of silvery or whitish; tail bicolor, although black all around near tip; tops of feet whitish or silvery; guard hairs, epecially on rump, long and conspicuous; ears short; skull small and not strongly arched in nasofrontal region; posterior margin of interparietal with a median notch formed by supraoccipital; palatine foramina short; no preoptic foramen (in front of optic foramen) usually; base of baculum nearly diamond-shaped and narrow."

Museum type specimens

Holotype: USNM 110333. Sigmodon ochrognathus. Adult female. Chisos Mountains, Brewster County, Texas. Collected 13 June 1901. Dorsal view of the skin.
Holotype: USNM 110333. Sigmodon ochrognathus. Adult female. Chisos Mountains, Brewster County, Texas. Collected 13 June 1901. Ventral view of the skin.

External measurements

Length measurements are in millimeters (mm) and weight measurements are in grams (g), unless stated otherwise. If available, the sample size (n=) is provided. If a range is not provided and n= is not given, then the listed measurement represents an average.

Part of range	Reference	Total length	Tail length	Hindfoot length	Ear length	Mass
Arizona (Santa Cruz and western Cochise cos.)	Hoffmeister (1986)	males: 188–251 (n=30); females: 193–264 (n=23)	males: 80–111 (n=30); females: 81–114 (n=23)	males: 25–30 (n=30); females: 25–30 (n=23)	males: 14–19 (n=30); females: 15–18 (n=23)
not reported	Ceballos (editor, 2014)	192–243	85–110	26–30	16–21	41–133
Texas	Schmidly & Bradley (2016)	259	114	28		50–80, occasionally as much as 112

Skull

Holotype: USNM 110333. Sigmodon ochrognathus. Adult female. Chisos Mountains, Brewster County, Texas. Collected 13 June 1901. Dorsal view of the skull.
Holotype: USNM 110333. Sigmodon ochrognathus. Adult female. Chisos Mountains, Brewster County, Texas. Collected 13 June 1901. Ventral view of the skull.
Holotype: USNM 110333. Sigmodon ochrognathus. Adult female. Chisos Mountains, Brewster County, Texas. Collected 13 June 1901. Lateral view of the skull.
Holotype: USNM 110333. Sigmodon ochrognathus. Adult female. Chisos Mountains, Brewster County, Texas. Collected 13 June 1901. Dorsal view of the mandible.
Holotype: USNM 110333. Sigmodon ochrognathus. Adult female. Chisos Mountains, Brewster County, Texas. Collected 13 June 1901. Lateral view of the left mandible.
Holotype: USNM 110333. Sigmodon ochrognathus. Adult female. Upper molars.
Holotype: USNM 110333. Sigmodon ochrognathus. Adult female. Lower molars.

Similar species

From Hoffmesiter (1986): "S. ochrognathus differs from S. arizonae and S. hispidus in the presence of a yellow nose and eye ring; smaller size, especially the hind foot (30 mm or less). S. fulviventer differs from S. ochrognathus as follows: underparts brownish, buffy, or fulvous rather than whitish; dorsum speckled or "salt and peppery"; tops of feet buffy; tail blackish or nearly so all around."

From Schmidly & Bradley (2016): "Similar to S. hispidus but paler and with the snout distinctly orange or rusty; tail hairier and distinctly bicolor, nearly black above, grayish buff below; underparts grayish white."

Arizona Cotton Rat (Sigmodon arizonae) photographed by Gordon Karre in Gilbert, Arizona. Sigmodon hispidus and Sigmodon arizonae look superficially similar but their ranges are mostly non-overlapping.
Tawny-bellied Cotton Rat (Sigmodon fulviventer) observed by Ricardo Arredondo T. in Coeneo, Michoacán, México. Sigmodon fulviventer has underparts that are distinctly brownish, buffy, or fulvous, extending from throat to anus.
Hispid Cotton Rat (Sigmodon hispidus) observed by Bob Oswald in Gainesville, Florida. Sigmodon hispidus and Sigmodon arizonae look superficially similar but their ranges are mostly non-overlapping.
Yellow-nosed Cotton Rat (Sigmodon ochrognathus) observed by Randy Babb. Sigmodon ochrognathus has a conspicuous "yellow" nose.

References

Bailey V. 1902. Synopsis of the North American Species of Sigmodon. Proceedings of the Biological Society of Washington 15, 115.

Ceballos G, editor. 2014. Mammals of Mexico. Baltimore (MD, USA): Johns Hopkins University Press.

Hoffmeister DF. 1986. Mammals of Arizona. Tucson (AZ, USA): University of Arizona Press.

Schmidly DJ, Bradley RD. 2016. The mammals of Texas. Austin (TX, USA): University of Texas Press.