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Chaetodipus intermedius

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

The Rock Pocket Mouse (Chaetodipus intermedius) is a small pocket mouse typically found on rocky slopes or in areas with rocky and gravelly soils. In Arizona, Hoffmeister (1986) noted that the species was largely restricted to rocky slopes.

Description

From Hoffmeister (1986): "Spines present on rump, but often difficult to detect; hind foot short, usually 22 mm or less; tail with a terminal tuft and bicolored; color of dorsum darkish, varying from grayish buff to dark brownish-black to black."

Ears have a lobed antitragus (projection of cartilage at the inner base of the ear).

Rock Pocket Mouse (Chaetodipus intermedius) photographed by Rick Overson and Laura Steger on Black Butte near the Vulture Mountains of Maricopa County, Arizona.
ASUMAC008873. Rock Pocket Mouse (Chaetodipus intermedius) from the Sand Tank Mountains of Maricopa County, Arizona.
ASUMAC008873. Arrows point to a few of the many rump spines of the Rock Pocket Mouse (Chaetodipus intermedius).

Museum specimens

  • Holotype: USNM 186509. Chaetodipus intermedius intermedius. Adult male. Mud Spring, [Mohave County], Arizona. Collected 26 February 1889.
  • Holotype: USNM 186509. Chaetodipus intermedius intermedius. Adult male. Mud Spring, [Mohave County], Arizona. Collected 26 February 1889.
  • Holotype: USNM 564498. Chaetodipus intermedius beardi. Adult female. Twenty-six miles (42 km) north, 15.5 mi (25 km) east Engle, Socorro County, New Mexico. Collected 23 August 1982.
  • Holotype: USNM 564498. Chaetodipus intermedius beardi. Adult female. Twenty-six miles (42 km) north, 15.5 mi (25 km) east Engle, Socorro County, New Mexico. Collected 23 August 1982.

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
not reported Ceballos (editor, 2014) 152–180 83–103 19–24 7–12 10–19
Texas Schmidly & Bradley (2016) 180 103 23 12–18


Color variation

Borrowed from Hoekstra et al. (2005): "Phenotypic variation across the range of Chaetodipus intermedius in the southwestern US. Photographs represent the typical dorsal coloration of individuals from each of 14 collecting locales indicated by circles. Filled circles represent lava flows and open circles are nonvolcanic rocky regions. The border between Arizona and New Mexico roughly represents the interface of the Sonoran and Chihuahuan deserts, respectively."
Borrowed from Hoekstra & Nachman (2005): "Coat color variation within rock pocket mice, Chaetodipus intermedius. The melanic mice in each pair were caught on lava, while the light mice in each pair were caught on nearby light-colored rocks."

Skull

From Hoffmeister (1986): "anterior edge of interparietal nearly straight, not angled forward; supraoccipital forms a sharp-angled wedge between interparietal and bullae; bullae moderately inflated, almost extending posteriorly to place of occiput; rostrum relatively narrow..."

  • Holotype: USNM 203003. Chaetodipus intermedius phasma. Adult female. Tinajas Altas, [Gila Mountains], Yuma County, Arizona. Collected 23 November 1913. Dorsal view of skull.
  • Holotype: USNM 203003. Chaetodipus intermedius phasma. Arrows identify the interorbital width. The interparietal bone is colored yellow. The interparietal with is greater than the interorbital width (Hoffmeister, 1986).
  • Holotype: USNM 203003. Chaetodipus intermedius phasma. Adult female. Tinajas Altas, [Gila Mountains], Yuma County, Arizona. Collected 23 November 1913. Ventral view of skull.
  • Holotype: USNM 203003. Chaetodipus intermedius phasma. Adult female. Tinajas Altas, [Gila Mountains], Yuma County, Arizona. Collected 23 November 1913. Lateral view of skull.
  • Holotype: USNM 203003. Chaetodipus intermedius phasma. Adult female. Tinajas Altas, [Gila Mountains], Yuma County, Arizona. Collected 23 November 1913. Dorsal view of the mandible.
  • Holotype: USNM 203003. Chaetodipus intermedius phasma. Adult female. Tinajas Altas, [Gila Mountains], Yuma County, Arizona. Collected 23 November 1913. Lateral view of the left mandible.
  • Holotype: USNM 203003. Chaetodipus intermedius phasma. Adult. Upper molars.
  • Holotype: USNM 203003. Chaetodipus intermedius phasma. Adult. Lower molars.
  • Holotype: USNM 203003. Chaetodipus intermedius phasma. Adult. The interparietal (in yellow) is not in contact with the bullae and is separated by narrow projections of parietals and supraoccipitals. Black arrows point to the narrow projections of the supraoccipitals in blue. The narrow projections of the parietals are shown in green.

Habitat

From Hoffmeister (1986): "intermedius is "strongly restricted to rocks and rocky habitats, mostly in the creosote bush-saltbush desertscrub. Without a rocky situation, intermedius should not be expected." The color of the dorsum in intermedius can vary based on the color of substrate.

Similar species

In the USA, Chaetodipus intermedius is sympatric or near-sympatric with the following species of pocket mice: Bailey's Pocket Mouse (Chaetodipus baileyi), Highland Coarse-haired Pocket Mouse (Chaetodipus collis), Chihuahuan Desert Pocket Mouse (Chaetodipus eremicus), Long-tailed Pocket Mouse (Chaetodipus formosus), Desert Pocket Mouse (Chaetodipus penicillatus), Arizona Pocket Mouse (Perognathus amplus), Plains Pocket Mouse (Perognathus flavescens), Silky Pocket Mouse (Perognathus flavus), and Merriam's Pocket Mouse (Perognathus merriami).

Comparison with Chaetodipus baileyi

From Hoffmeister (1986): "C. intermedius differs from C. baileyi in rump spines present; hind foot shorter (less than 26 mm); body shorter; interorbital breadth less than interparietal breadth; skull shorter and narrower; skull less deep (under 10.0 mm)." Additionally, C. intermedius is "strongly restricted to rocks and rocky habitats, mostly in the creosote bush-saltbush desertscrub. Without a rocky situation, intermedius should not be expected." The color of the dorsum in intermedius can vary based on the color of substrate.

  • Rock Pocket Mouse (Chaetodipus intermedius)
  • Bailey's Pocket Mouse (Chaetodipus baileyi)
  • Holotype: 203003. Chaetodipus intermedius phasma. Arrows identify the interorbital width. The interparietal bone is colored yellow. The interparietal with is greater than the interorbital width (Hoffmeister, 1986).
  • Holotype: 17838/24775. Chaetodipus baileyi baileyi. Arrows identify the interorbital width. The interparietal bone is colored yellow. The interorbital width is greater than the width of the interparietal (Hoffmeister, 1986).

Comparison with Chaetodipus collis

  • Rock Pocket Mouse (Chaetodipus intermedius) photographed by Rick Overson and Laura Steger on Black Butte near the Vulture Mountains of Maricopa County, Arizona.
  • Arrows point to a few of the many rump spines of the Rock Pocket Mouse (Chaetodipus intermedius).
  • Highland Coarse-haired Pocket Mouse (Chaetodipus collis) observed by Madison Gover. The white arrow points to the subauricular spot, which is sometimes present in this species. When it is present, it is small. The black arrow points to one of the many rump spines.

Comparison with Chaetodipus eremicus

Chaetodipus intermedius is a rock-dwelling pocket mouse and the restriction to rocky situations will usually separate this species from the Chihuahuan Desert Pocket Mouse (Chaetodipus eremicus) (CMDBS, 2008). Chaetodipus eremicus is similar in size to C. intermedius. C. intermedius has rump spines, but these may be difficult to detect (CMDBS, 2008).

  • Rock Pocket Mouse (Chaetodipus intermedius)
  • Chihuahuan Desert Pocket Mouse (Chaetodipus eremicus)
  • Holotype: 203003. Chaetodipus intermedius phasma. Arrows identify the interorbital width. The interparietal bone is colored yellow. The interorbital region is narrower than the width of the interparietal (Hoffmeister, 1986).
  • Holotype: 21052/36094. Chaetodipus eremicus eremicus. Arrows identify the interorbital width. The interparietal bone is colored yellow. The interorbital region is narrower than the width of the interparietal.
  • Rock Pocket Mouse (Chaetodipus intermedius). The interparietal (in yellow) is not in contact with the bullae and is separated by narrow projections of parietals and supraoccipitals. Black arrows point to the narrow projections of the supraoccipitals in blue. The narrow projections of the parietals are shown in green. The anterior edge of the interparietal nearly straight, not angled forward.
  • Holotype: 21052/36094. Chaetodipus eremicus eremicus. The interparietal (in yellow) is not in contact with mastoid bullae and is separated by narrow projections of parietals and supraoccipitals. Black arrows point to the narrow projections of the supraoccipitals in blue. The narrow projections of the parietals are shown in green. The anterior edge of the interparietal is angled forward.

Comparison with Chaetodipus formosus

From Hoffmeister (1986), the Long-tailed Pocket Mouse (Chaetodipus formosus) differs from Chaetodipus intermedius in: "longer tail, with the interorbital width greater than the interparietal width rather than the reverse." Additionally, C. intermedius has rump spines, but they may be difficult to detect.

  • Rock Pocket Mouse (Chaetodipus intermedius)
  • Long-tailed Pocket Mouse (Chaetodipus formosus)
  • Holotype: 203003. Chaetodipus intermedius phasma. Arrows identify the interorbital width. The interparietal bone is colored yellow. The interparietal with is greater than the interorbital width (Hoffmeister, 1986).
  • Holotype: 186508. Chaetodipus formosus formosus. Arrows identify the interorbital width. The interparietal bone is colored yellow. The interorbital width is greater than the interparietal width (Hoffmeister, 1986).

Comparison with Chaetodipus penicillatus

From Hoffmeister (1986): "[Chaetodipus] intermedius differs from penicillatus, the species with which it is most frequently confused, in the presence of spinelike hairs on the rump; hind foot usually 22 mm or less rather than more; interparietal with straight rather than angled suture along anterior face, and thus not pentagonal or five-sided; extensions of anterior wings of supraoccipital between interparietal, and bullae wedge-shaped rather than truncate; rostrum narrower."

  • Rock Pocket Mouse (Chaetodipus intermedius)
  • Desert Pocket Mouse (Chaetodipus penicillatus)
  • Rock Pocket Mouse (Chaetodipus intermedius). The interparietal (in yellow) is not in contact with the bullae and is separated by narrow projections of parietals and supraoccipitals. Black arrows point to the narrow projections of the supraoccipitals in blue. The narrow projections of the parietals are shown in green. The anterior edge of the interparietal nearly straight, not angled forward.
  • The interparietal of the Desert Pocket Mouse (Chaetodipus penicillatus) is pentagonal with all angles somewhat rounded and does not contact the mastoid bullae (Hall, 1981; Mantooth and Best, 2005).

Comparison with pocket mice in the genus Perognathus

Chaetodipus intermedius is not easily confused with pocket mice in the genus Perognathus. The silky pocket mice (genus: Perognathus) generally have smoother pelage and softer appearance than the coarse-haired pocket mice (genus: Chaetodipus). All Perognathus species lack rump spines. The presence of rump spines and a tail with both a crest and tuft will help to differentiate Chaetodipus intermedius from sympatric silky pocket mice—Arizona Pocket Mouse (Perognathus amplus), Plains Pocket Mouse (Perognathus flavescens), Silky Pocket Mouse (Perognathus flavus), and Merriam's Pocket Mouse (Perognathus merriami).

  • Rock Pocket Mouse (Chaetodipus intermedius)
  • Arizona Pocket Mouse (Perognathus amplus). Coloration varies among subspecies but, in general, it is salmon-ochre on the back and yellowish-white on the abdomen.
  • Plains Pocket Mouse (Perognathus flavescens). Dorsal coloration ranges from buff to yellowish or reddish, with a variable dorsal wash of black hairs.
  • Silky Pocket Mouse (Perognathus flavus). Fur color varies depending on the subspecies and geographic location but typically ranges from yellowish-brown to grayish-brown.
  • Merriam's Pocket Mouse (Perognathus merriami). Dorsal color is yellowish or yellowish-orange, with a slight blackish tinge.

References

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

Hoekstra HE, Krenz JG, Nachman MW. 2005. Local adaptation in the rock pocket mouse (Chaetodipus intermedius): natural selection and phylogenetic history of populations. Heredity 94(2):217-228.

Hoekstra HE, Nachman MW. 2005. Adaptive coat color variation in rodents. Mammalian Diversification: From Chromosomes to Phylogeography, 133, 79.

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

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

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

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