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Key to the Regional Pocket Mice and Kangaroo Rats

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1. Soles of hind feet densely haired; interparietal less than greatest width of skull; maxilla with enlarged and laterally projecting flange above root of zygomatic arch: Dipodomys, 2

1'. Soles of hind feet naked, or furred only to plantar surface; interparietal more than greatest width of skull; maxilla with very small laterally projecting flange: 4

2. Maxillary breadth more than 22 mm; tip of tail white: Dipodomys spectabilis.

2'. Maxillary breadth less than 22 mm; tip of tail not white: 3

3. Hindfoot with four toes; lateral aspect of dentary ramus molded so as to suggest the bases of the teeth: Dipodomys merriami.

3'. Hindfoot with five toes; lateral aspect of dentary ramus flatter: Dipodomys ordii.

4. Bullae larger, in dorsal view comprising more than one-half of transverse distance across skull through middle of interparietal; hair on end of tail usually not longer than hair near base of tail: Perognathus, 5

4'. Bullae smaller, in dorsal view less than half of transverse distance across skull through middle of interparietal; hairs on end of tail longer than those at base or not: Chaetodipus, 8

5. Length of tail usually 60 mm or more; total length usually 120 mm or more; length of skull usually more than 21 mm; posterior bulge on supraoccipital prominent; rostrum short, heavy, and broad: 6

5'. Length of tail usually less than 60 mm; total length usually less than 120 mm; length of skull usually less than 21 mm; posterior supraoccipital bulge not prominent; rostrum long and narrow: 7.

6. Distribution east of the Pecos and upper Canadian rivers; morphological differences from P. apache not well marked: Perognathus flavescens

6'. Distribution west of the Pecos River; morphological differences from P. flavescens not well marked and sometimes considered a subspecies of P. flavescens: Perognathus apache

7. Distributed in southeastern New Mexico in Chaves and Eddy counties; may overlap with P. flavus in that area; morphological differences from P. flavus not well marked (sometimes considered as a subspecies of P. flavus): Perognathus merriami

7'. Distributed through most of New Mexico: Perognathus flavus

8. Hairs at end of tail not longer than those near base; tubes of auditory bullae projecting lateral of mastoids in dorsal view: Chaetodipus hispidus.

8'. Hairs at end of tail noticeably longer than those near base; tubes of auditory bullae not projecting as above: 9

9. Rump spines usually present; rocky habitats: 10

9'. Rump spines absent; habitat various: 11

10. Total length more than 180 mm; premaxilla extending distinctly farther posteriorly than nasal: Chaetodipus nelsoni.

10'. Total length less than 180 mm; premaxilla extending posteriorly about the same disance as nasal: Chaetodipus intermedius.

11. Tail much longer than head and body; head and body usually more than 95 mm; interparietal width equal to or less than least interorbital width: Chaetodipus baileyi.

11'. Tail slightly longer than head and body; head and body usually less than 95 mm; interparietal width exceeds least interorbital width: 12

12. Distribution to the west, barely entering into southwestern New Mexico near the Arizona border: Chaetodipus penicillatus.

12'. Throughout the Chihuahuan Desert region of the United States and south into Mexico: Chaetodipus eremicus. [C. penicillatus and C. eremicus are separated on molecular data rather than on external morphology.]

Key slightly modified from Findley (1987).

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Last Update: 26 Jul 2005