Geographic Distribution of the Pocket Mouse,

Perognathus fasciatus

BY

J. KNOX JONES, JR.

University of Kansas Publications

Museum of Natural History

Volume 5, No. 29, pp. 515-526, 7 figures in text

August 1, 1953

University of Kansas

LAWRENCE

1953

University of Kansas Publications, Museum of Natural History

Editors: E. Raymond Hall, Chairman, A. Byron Leonard,

Robert W. Wilson

Volume 5, No. 29, pp. 515-526, 7 figures in text

August 1, 1953

University of Kansas

Lawrence

1953

PRINTED BY

FERD VOILAND, JR., STATE PRINTER

TOPEKA. KANSAS

1953

24-7673

Geographic Distribution of the Pocket Mouse,

Perognathus fasciatus

BY

J. KNOX JONES, JR.

In his "Revision of the pocket mice of the genus Perognathus," Osgood
(1900:18-20) reviewed the distribution, as then known, of Perognathus
fasciatus and recognized two geographic races—Perognathus fasciatus
[fasciatus] Wied-Neuwied in eastern Montana and Wyoming and adjacent
parts of North and South Dakota, and Perognathus fasciatus infraluteus
Thomas, known only from the type locality at Loveland, Larimer County,
Colorado. Later, Cary (1911:61) described Perognathus fasciatus litus
as a pale subspecies occurring in the lower Sweetwater Valley and
adjacent parts of the Red Desert of south-central Wyoming. After 1911 no
important taxonomic contributions dealing with Perognathus fasciatus
appeared.

In studying the kinds of pocket mice known from Nebraska, I examined
thirteen specimens of P. fasciatus from the northwestern part of the
state which did not agree satisfactorily with the descriptions of any
known subspecies of fasciatus. This impelled me to examine material
from the entire range of P. fasciatus. This examination revealed that:
(1) Perognathus callistus Osgood, heretofore considered to be a full
species, should be reduced to subspecific rank under P. fasciatus; and
(2) specimens from eastern Wyoming and adjacent parts of Montana, South
Dakota and Nebraska represent an heretofore unrecognized subspecies.
Further investigation, however, revealed that Perognathus flavescens
olivaceogriseus Swenk, described from northwestern Nebraska (Swenk,
1940:6), is not flavescens but actually fasciatus. Since the
specimens on which Swenk's description was based were taken within the
range of this newly recognized subspecies, and since my examination of
the holotype shows it to be of the species Perognathus fasciatus, the
subspecific name olivaceogriseus is available.

[Pg 518]

The subspecies of P. fasciatus are most easily distinguished by color
of pelage, in which there is a general cline from northeast (dark) to
southwest (pale). Cranially, the subspecies are less distinct. The
skulls of P. f. callistus can be distinguished from those of the other
subspecies by several differences; however, among the other four
subspecies, only minor cranial differences are evident. Individual
variation was found to be greater than secondary sexual variation.

Fig. 1. Distribution of the five subspecies of
Perognathus fasciatus. Solid symbols represent specimens examined;
circled symbols represent type localities.



Guide to subspecies

1. P. f. fasciatus

2. P. f. olivaceogriseus

3. P. f. infraluteus

4. P. f. litus

5. P. f. callistus

Perognathus fasciatus fasciatus Wied-Neuwied

Remarks.—For comparisons with Perognathus fasciatus
olivaceogriseus, geographically adjacent to the southwest, see account
of that subspecies.

Specimens from the eastern part of the range of P. f. fasciatus are
somewhat smaller and slightly darker than topotypes from Buford, North
Dakota. Specimens from 9 mi. SE Bainville, Johnson Lake and 3 mi. S
Medicine Lake, Montana, and from Crosby, North Dakota, are also paler
than those from farther east. At the southern limit of the range of the
subspecies, specimens from the Rosebud Agency and Minichaduza River,
South Dakota, approach olivaceogriseus in pale dorsal coloration.

Perognathus fasciatus olivaceogriseus Swenk

Remarks.—From topotypes of Perognathus fasciatus fasciatus,
geographically adjacent to the northeast, P. f. olivaceogriseus
differs in: Upper parts paler, especially face which is heavily washed
with buff; hind foot smaller; skull averaging slightly smaller in all
measurements taken (especially least interorbital breadth and cranial
depth), except mastoidal breadth which is slightly more and
interparietal breadth, length of tympanic bulla and length of maxillary
tooth-row which are approximately the same. From topotypes of
Perognathus fasciatus infraluteus, geographically adjacent to the
south, P. f. olivaceogriseus differs in: Upper parts paler and less
drab; lateral line brighter and more ochraceous; underparts never buffy;
skull averaging larger in all measurements taken except interparietal
breadth and length of maxillary tooth-row which are smaller. From
topotypes of Perognathus fasciatus litus, geographically adjacent to
the southwest, P. f. olivaceogriseus differs in: Upper parts darker;
skull, when specimens of equal age are compared, averaging larger in
mastoidal breadth, interparietal breadth and basal length. From
topotypes of Perognathus fasciatus callistus, P. f. olivaceogriseus
differs in: Upper parts slightly darker, pelage not silky, coarser in
appearance; hind foot shorter; skull averaging smaller in all
measurements taken (especially mastoidal breadth), except interparietal
breadth which is more.

[Pg 521]

Swenk (loc. cit.) originally described P. f. olivaceogriseus as a
subspecies of Perognathus flavescens. I have examined the holotype,
kindly made available to me by Dr. Seth B. Benson of the Museum of
Vertebrate Zoology, University of California, and the paratype, in the
collection of the University of Nebraska State Museum. Neither is P.
flavescens, but both are clearly specimens of P. Fasciatus on the
basis of olive-gray dorsal coloration, larger over-all dimensions of the
skull, and in that the tympanic bullae do not meet anteriorly. In
addition, a third specimen from Glen, Nebraska, purported by Swenk to be
intermediate between flavescens and olivaceogriseus, has been
examined and found to be an immature fasciatus.

Figs. 2-7. Skulls of two species of pocket mice. All ×
1-1/2. In comparison with P. flavescens note that P. fasciatus has
the tympanic bullae separated anteriorly and that the skull is slightly
larger in over-all dimensions.


Figs. 2-4. Perognathus fasciatus fasciatus. Buford, Williams County,
North Dakota, May 6, 1910, [** Male], No. 168599 USBS.


Figs. 5-7. Perognathus flavescens flavescens, Kennedy, Cherry County,
Nebraska, July 9, 1935, [** Female], No. 66883 MVZ.]

In the original description Swenk indicated the type locality as
Chadron, Dawes County, Nebraska. The locality given on the specimen
label of the holotype, however, is 5 mi. E Chadron. In addition, Swenk
(loc. cit.), in the paragraph preceding the description of[Pg 522]
olivaceogriseus, states that the holotype was actually taken on Little
Bordeaux Creek, sec. 14, T. 33 N, R. 48 W, 3 mi. E Chadron, on the farm
of L. M. Gates, who obtained the holotype. It seems best to restrict the
type locality to the place last mentioned.

Four specimens from southeastern Alberta recently reported by Moore
(1953:143) have been examined and seem best referred, among known
subspecies of fasciatus, to P. f. olivaceogriseus. They differ from
the latter in several minor cranial features and more drab back, sides
and lateral line. When adequate material is available they may prove to
be subspecifically different from olivaceogriseus. Moore referred
these specimens to P. f. fasciatus.

Specimens from extreme northwestern Nebraska, including the holotype,
are slightly darker than specimens from eastern Wyoming. A specimen from
Ft. Steele, Wyoming, shows approach to P. f. litus in pale dorsal
coloration.

Perognathus fasciatus infraluteus Thomas

Remarks.—For comparisons with Perognathus fasciatus olivaceogriseus
Swenk, geographically adjacent to the north, see the preceding account
of that subspecies on page 520.

[Pg 523]

Of the seven topotypes available to me, six show various degrees of
encroachment of the color of the lateral line upon the underparts,
giving the ventral surface a buffy appearance, the "distinguishing
character" of the subspecies according to Osgood (op. cit.:20). When
additional specimens are available, this character may be found to be
one of individual variation, although no specimens from other parts of
the range of the species have been found to exhibit it. Of the
subspecies P. f. infraluteus, each of the eight specimens examined by
me possesses buffy subauricular patches.

The specimen from 7 mi. N Ramah, Colorado, is slightly darker and less
drab than the topotypes and does not possess buffy underparts. The skull
of the specimen is broken but on the basis of characters of the pelage
it seems to be intermediate between infraluteus and olivaceogriseus
and is referred to the former on geographic grounds.

Perognathus fasciatus litus Cary

Remarks.—For comparisons with Perognathus fasciatus
olivaceogriseus, geographically adjacent to the northeast, see account
of that subspecies. From Perognathus fasciatus callistus,
geographically adjacent to the southwest, P. f. litus differs in:
Upper parts paler with no trace of olivaceous; hind foot shorter; skull,
when specimens of equal age are compared, averaging smaller in all
measurements taken (especially occipitonasal length, mastoidal breadth,
length of tympanic bulla and cranial depth), except interparietal
breadth which is more.

No fully adult specimens of P. f. litus have been available to me for
this study. Two of the three specimens mentioned by Cary in the original
description (holotype not seen) have been examined and found to possess
adult pelage, but cranially they must be classed as young adults. These
specimens are paler than those of any other subspecies of fasciatus
and do not have the olivaceous dorsal coloration present in other
subspecies.

P. f. litus is seemingly an endemic race in the lower Sweetwater
Valley and adjacent parts of the Red Desert, Wyoming. The type locality,
recorded by Cary in the original description as "Sun, Sweetwater Valley,
Wyoming," is here placed in Natrona County on the[Pg 524] basis of the map
(frontispiece) in Cary's (1917) "Life Zone Investigations in Wyoming."

Perognathus fasciatus callistus Osgood

Remarks.—For comparisons with Perognathus fasciatus litus,
geographically adjacent to the north, see account of that subspecies.

When Osgood (loc. cit.) described P. f. callistus as a full species,
he characterized it as having " ... the attractive coloration of
fasciatus, but softer and more delicate. Its position is evidently
between fasciatus and apache, and its nearest relations are clearly
with the latter." He further remarked that, "Its large size immediately
separates it from fasciatus which it resembles externally, especially
before maturity."

Comparison of the average and extreme external measurements of ten adult
P. f. callistus from Sweetwater County, Wyoming, with adult
individuals of other subspecies of P. fasciatus shows that callistus
does not average larger than P. f. olivaceogriseus except in length of
hind foot and that it averages slightly smaller in all external
measurements than topotypes of P. f. fasciatus. Moreover, judging from
the accounts of Goldman (1918:24) and Durrant (1952:235), Perognathus
apache caryi (the subspecies of P. apache nearest to the range of P.
f. callistus) is significantly larger externally and has no trace of
olivaceous in the dorsal pelage.

Comparison of the skulls of callistus with a skull of Perognathus
apache apache from Wingate, New Mexico (USBS 137388), reveals the
following differences: Interparietal bone wider in callistus,
averaging 4.5 (as opposed to 4.0) and more pentagonal; lacrimal bone
shorter and stouter in callistus; tympanic bullae more inflated in
callistus; interorbital foramina larger in callistus; lower premolar
approximately the same size as the last lower molar in callistus,
approximately half the size of the last lower molar in apache.
Conversely, comparison of skulls of callistus with those of P.
fasciatus as concerns the above mentioned features reveals that they
closely resemble each other. In view of this resemblance it seems best
to arrange callistus as a subspecies of P. fasciatus.

[Pg 525]

P. f. callistus is distinct cranially from all other subspecies of P.
fasciatus in the narrowness of the interparietal, the greater length of
the tympanic bulla and the greater mastoidal breadth. The fine, silky
nature of the pelage is shared, to some extent, with P. f. litus.

A specimen from 27 mi. N, 37 mi. E Rock Springs, Wyoming, referred to
callistus resembles litus in pale dorsal coloration and slightly
wider interparietal. Four immature specimens from 25 mi. N, 38 mi. E
Rock Springs, also referred to callistus, have extremely pale juvenal
pelage and also are judged to be intergrades with litus.

TABLE LEGEND:

Column A: Sex and number of individuals averaged or catalog number

Column B: Occipitonasal length

Column C: Frontonasal length

Column D: Basal length[1]

Column E: Mastoidal breadth

Column G: Interorbital breadth

Column H: Interparietal breadth

Column I: Cranial depth

Column J: Length of tym. bulla

Column K: Length of maxillary tooth-row



Symbols:

: Male

: Female

[Pg 526]

LITERATURE CITED

Cary, M.

1911. A new pocket mouse from Wyoming. Proc. Biol. Soc. Washington,
24:61, March 22.
1917. Life Zone investigations in Wyoming. N. Amer. Fauna, 42:1-95,
October 3.

Durrant, S. D.
1952. Mammals of Utah, taxonomy and distribution. Univ. Kansas
Publ., Mus. Nat. Hist., 6:1-549, August 10.

Goldman, E. A.
1918. Five new mammals from Arizona and Colorado. Proc. Biol. Soc.
Washington, 31:21-26, May 16.

Moore, J. E.
1953. Notes on three additions to the rodent fauna of Alberta.
Canadian Field Nat., 66:142-143, February 28.

Osgood, W. H.
1900. Revision of the pocket mice of the genus Perognathus. N.
Amer. Fauna, 18:1-72, September 20.

Swenk, M. H.
1940. A study of the geographical and ecological distribution of
the buffy plains pocket mouse (Perognathus flavescens flavescens),
with description of a new subspecies from Nebraska. Missouri Valley
Fauna, 3:1-8, June 5.

University of Kansas Museum of Natural History, Lawrence, Kansas.
Transmitted, April 20, 1953.

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