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Chaetodipus fallax

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San Diego Pocket Mouse
(Chaetodipus fallax)
Range
Taxonomic classification
Order:Rodentia
Suborder:Supramyomorpha
Infraorder:Castorimorphi
Superfamily:Geomyoidea
Family:Heteromyidae
Subfamily:Perognathinae
Genus:Chaetodipus
Binomial details
Chaetodipus fallax (C. H. Merriam, 1889)
Other resources
Full taxonomic details at MDD

The San Diego Pocket Mouse (Chaetodipus fallax) is a medium-sized pocket mouse found in desert and coastal habitats in southern California, Baja California, and a few places in Baja California Sur, Mexico.

Description

From Lackey (1996): "Chaetodipus fallax is medium in size compared with other species of the genus. The upper parts of the pelage are rich brown, darker over the rump, and under parts are white or creamy white. Bristles on the rump are black, whereas those on the flank are white. The lateral line and subterminal portions of hairs of the upper parts are pinkish buff. The tail is long and crested, dark above and white below. The ears are dusky on the inflexed portion, and whitish on the inner surface."

From Jameson & Peeters (2004): A medium-sized, brownish pocket mouse. There are conspicuous white, spiny hairs on the dorsum and sides and black spines on the rump. A buff stripe, or lateral line, separates the venter and dorsum. The tail is bicolored and crested. The heel of the hind foot is naked.

San Diego Pocket Mouse (Chaetodipus fallax) observed by Caleb Villar in Riverside County, California.
San Diego Pocket Mouse (Chaetodipus fallax) observed by Alyssa Semerdjian in Rancho Jamul Ecological Reserve, San Diego County, California. The white arrow points to the lobed antitragus of the ear. Black arrows point to one of each of the many white and black spiny hairs.

Museum specimens

  • Holotype: 15889/22684. Chaetodipus fallax fallax. Adult male. San Bernardino County, California. Collected 21 April 1887.
  • Holotype: 15889/22684. Chaetodipus fallax fallax. Adult male. San Bernardino County, California. Collected 21 April 1887.

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
California Jameson & Peeters (2004) 176–200 88–118 21–26 15–18
rangewide Lackey (1996) males: 191 (n=20); females: 187 (n=20) males: 106 (n=10); females: 105 (n=10) males: 24 (n=20); females: 23 (n=20) males: 10 (n=20); females: 10 (n=20)


Skull

From Lackey (1996): "The interparietal is pentagonal with a conspicuous anterior angle, the cranium is moderately arched, and the rostrum is attenuate and narrow... the interparietal is wide with the anterior angle obsolete, the mastoids are large, and the nasofrontal suture is slightly or not at all emarginate (Hall, 1981; Osgood, 1900; Ryan, 1968)."

  • Holotype: 15889/22684. Chaetodipus fallax fallax. Adult male. San Bernardino County, California. Collected 21 April 1887. Dorsal view of the skull.
  • Holotype: 15889/22684. Chaetodipus fallax fallax. Adult male. Arrows identify the interorbital width. The interparietal bone is colored yellow.
  • Holotype: 15889/22684. Chaetodipus fallax fallax. Adult male. San Bernardino County, California. Collected 21 April 1887. Ventral view of the skull.
  • Holotype: 15889/22684. Chaetodipus fallax fallax. Adult male. San Bernardino County, California. Collected 21 April 1887. Lateral view of the skull.
  • Holotype: 15889/22684. Chaetodipus fallax fallax. Adult male. San Bernardino County, California. Collected 21 April 1887. Dorsal view of the mandible.
  • Holotype: 15889/22684. Chaetodipus fallax fallax. Adult male. San Bernardino County, California. Collected 21 April 1887. Lateral view of the left mandible.
  • Holotype: 15889/22684. Chaetodipus fallax fallax. Adult. Upper molars.
  • Holotype: 15889/22684. Chaetodipus fallax fallax. Adult. Lower molars.

Similar species

In the USA, Chaetodipus fallax is sympatric with the following species of pocket mice: California Pocket Mouse (Chaetodipus californicus), Long-tailed Pocket Mouse (Chaetodipus formosus), Desert Pocket Mouse (Chaetodipus penicillatus), Peninsular Pocket Mouse (Chaetodipus rudinoris), Spiny Pocket Mouse (Chaetodipus spinatus) and Little Pocket Mouse (Perognathus longimembris). The presence of pronounced rump spines distinguishes fallax from pocket mice in the genus Perognathus and from the Long-tailed Pocket Mouse (Chaetodipus formosus) and the Desert Pocket Mouse (Chaetodipus penicillatus). The California Pocket Mouse (Chaetodipus californicus) and the Spiny Pocket Mouse (Chaetodipus spinatus) also have pronounced rump spines, but C.spinatus lacks a well-marked lateral line (Hall, 1981; Lackey, 1991). Addtionally, the rump spines of C. fallax are not nearly as well developed as in the Spiny Pocket Mouse (Chaetodipus spinatus), where they extend onto the shoulders (Patton and Alvarez-Castañeda, 1999). According to Patton and Alvarez-Castañeda (1999), when comparing the California Pocket Mouse (Chaetodipus californicus) with fallax, californicus is "distinctly larger in size, with longer and obviously more square-topped as opposed to rounded ears."

  • San Diego Pocket Mouse (Chaetodipus fallax) observed in Riverside County, California, by Caleb Villar. The lateral line is pinkish buff in this species.
  • San Diego Pocket Mouse (Chaetodipus fallax) observed by Alyssa Semerdjian in Rancho Jamul Ecological Reserve, San Diego County, California. Black arrows point to one of each of the many white and black spiny hairs. The white arrow points to the lobed antitragus of the ear, which is present in all species in the genus Chaetodipus.
  • Spiny Pocket Mouse (Chaetodipus spinatus) observed by Charles A. Drost and Jan Hart, USGS. The lateral line is faint or absent in this species.
  • California Pocket Mouse (Chaetodipus californicus). Arrow points to the well-defined, buff-colored lateral line.
  • The ears of the California Pocket Mouse (Chaetodipus californicus) are more square-topped (as the black lines attempt to show) as opposed to rounded. Original image by Boaz Benaiah Solorio.

References

Hall ER. 1981. The mammals of North America. 2 vols. John Wiley and Sons, New York.

Jameson EW, Peeters HJ. 2004. Mammals of California (No. 66). Berkeley (CA, USA): University of California Press.

Lackey JA. 1996. Chaetodipus fallax. Mammalian Species (517):pp.1-6. https://doi.org/10.2307/3504127

Patton JL, Alvarez-Castañeda ST, editors. 1999. Family Heteromyidae. Mamiferos del noroeste de México. La Paz (Baja California Sur, MX): Centro de Investigaciones Biológicas del Noroeste.

Merriam CH. 1889. Revision of the North American pocket mice. North American Fauna 1:1-29.

Osgood WH. 1900. Revision of the pocket mice of the genus Perognathus. North American Fauna 18:1-73.

Ryan RM. 1968. Mammals of Deep Canyon, Colorado -Desert, California. The Desert Museum, Palm Springs, California.

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