University of Kansas Publications

Museum of Natural History

Volume 9, No. 21, pp. 539-548

January 14, 1960

Pleistocene Pocket Gophers

From San Josecito Cave,

Nuevo León, México

BY

ROBERT J. RUSSELL

University of Kansas

Lawrence

1960

University of Kansas Publications, Museum of Natural History

Editors: E. Raymond Hall, Chairman, Henry S. Fitch,

Robert W. Wilson

Volume 9, No. 21, pp. 539-548

Published January 14, 1960

University of Kansas

Lawrence, Kansas

PRINTED IN

THE STATE PRINTING PLANT

TOPEKA, KANSAS

1960

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[Pg 541]

Pleistocene Pocket Gophers

From San Josecito Cave, Nuevo León, México

BY

ROBERT J. RUSSELL

Cueva de San Josecito in the province of Aramberri, near the
town on Aramberri, Nuevo León, México, is at an elevation of
approximately 7400 feet above sea level on the east-facing slope
of the Sierra Madre Occidental in a limestone scarp. The dominant
vegetation about the cave is the decidedly boreal forest association
of pine and live oak. Additional information concerning the cave
is provided by Miller (1943:143-144).

Animal remains recovered from San Josecito Cave are among the
most important Pleistocene finds in México, and include the most
extensive collection of Pleistocene geomyids. The vertebrate remains
are probably late Pleistocene in age; certainly they are post-Blancan,
since the genera Equus, Preptoceras, Smilodon, and Aenocyon
(all Pleistocene genera) are present. According to Miller's
(loc. cit.:145) extensive report on the avifauna, the bird remains
from the cave are a remarkable assemblage and beautifully preserved.
Most of the mammalian remains have been studied in
detail, and the results of these studies have been published in a
number of papers each treating specific groups. These reports
provide valuable information concerning the distribution of mammals
in northeastern México in the late Pleistocene, a knowledge of
which is most important to an understanding of present patterns of
distribution and evolution of Mexican mammals.

Cushing's (1945:182-185) report on his study of the rodents and
lagomorphs includes a description of an extinct pygmy species of
rabbit, Sylvilagus leonensis. He records three kinds of pocket
gophers from San Josecito; Cushing was able to separate the genus
Thomomys from two unidentified geomyids (loc. cit.:185). These
prove to belong to the genera Cratogeomys and Heterogeomys; the
materials are described below. Cushing records also larger mammals,
including the antilocaprid (Stockoceros conklingi), saber-toothed
cat (Smilodon), dire wolf (Aenocyon), a large oviboid
(Preptoceras), and deer (loc. cit.:182).

More recently Findley (1953:633-639) has written on the remains
of the family Soricidae taken from the cave, and Hooper (1952:59)[Pg 542]
has studied the bones of the genus Reithrodontomys and found them
not different from those of R. megalotis that inhabits the region of
the cave today. Handley (1955:48) has described a new species of
plecotine bat, Corynorhinus tetralophodon, from the collection.
Jones (1958:389-396) published an account of the bats of San Josecito,
and described a new vampire bat, Desmodus stocki, from the
cave. Jakway (1958:313-327) has reported on the lagomorphs and
rodents in detail, and compared this part of the cave fauna with
that of Rancho La Brea and Papago Spring Cave, Arizona. Jakway
(lit. cit.:323-324) suggests that the fauna from San Josecito is late
Pleistocene, probably contemporaneous with the remains from
Papago Spring Cave and pre-Rancholabrean.

Material referable to Thomomys consists of a nearly complete
cranium, L.A.C.M. (C.I.T.) No. 3952, with nasals, maxillary teeth,
and lower parts of braincase missing and zygomata broken; four
rami (unnumbered), one of which is badly broken; and two isolated
molariform teeth. The skull has a sphenoidal fissure, a feature
typical of the umbrinus group of Thomomys. The fossil specimens
closely approximate in size the living subspecies Thomomys umbrinus
analogus Goldman. Thomomys is not known from the vicinity
of the cave at the present time and has not been reported
from southwestern Nuevo León, even though there has been
extensive collecting for pocket gophers there in recent years. To
my knowledge the nearest record of occurrence of modern Thomomys
is a series of Thomomys umbrinus analogus from 12 miles east
of San Antonio de las Alazanas at an elevation of 9000 feet in the
state of Coahuila (Baker, 1953:511), approximately 85 miles to the
northwest. The fossil gophers are not from the talus of the cave
floor, which is evidently of subrecent origin, but from the Pleistocene
deposits below. Close resemblance to the living subspecies T. u.
analogus, however, indicates that these remains are not so old as
some of the other geomyid fossils from the cave.

[Pg 543]

Seven rami pertain to the genus Cratogeomys. All except three,
L.A.C.M. (C.I.T.) Nos. 2974, 2978, and 3954, lack cheek teeth
and the posterior processes are missing on most of the mandibles.
No. 2974 is smaller than the other specimens, and probably is from
a young individual. No. 3954 may have been fossilized at an earlier
date than the other six jaws; however, it is comparable to them in
size and morphology. Also present in the deposits are three limb
bones of Cratogeomys castanops. One, a right humerus bearing
L.A.C.M. (C.I.T.) No. 2982, is slightly larger than that of the
pocket gophers living in the area now. Two tibias, L.A.C.M.
(C.I.T.) Nos. 2983 and 2984, complete the material referable to
this species.

Cratogeomys castanops planifrons (see Russell and Baker, 1955:607)
occurs in the immediate vicinity of San Josecito today. None
of the rami from the cave differs appreciably from those of the
subnubilus group of Cratogeomys castanops, a group of small subspecies
including planifrons, subnubilus, rubellus and peridoneus.
All are small in external measurements and skull and differ markedly
in this respect from the group of large subspecies (the subsimus
group) that occurs farther northward in Coahuila and Nuevo León.

A rostral part of a skull, L.A.C.M. (C.I.T.) No. 2927, is referable
to the genus Cratogeomys. This fragment consists of the
anterior part of the skull, including a portion of the frontals, the
premaxillae, a small part of the left maxilla, and the anterior parts
of the palatines. The nasals are missing, but both incisors are in
place including most of the roots. The single median sulcus on the
anterior face of each incisor is typical of the genus Cratogeomys.
The rostrum is long (25.8), as great in length as in the largest
subspecies of the subsimus group of Cratogeomys castanops (see
previous account for explanation) and as long as the rostrum of
Cratogeomys perotensis which is now known only from Veracruz,
México. The length of the rostrum was measured from the most
anterior median projection of the premaxillary to the most posterior
dorsal projection of the same bone. Actually, and especially in
relation to its length, the rostrum of the fossil is remarkably narrow.
The breadth of the rostrum measures 10.4, which is comparable to
that in the subnubilus group of small subspecies, and less than that[Pg 544]
(11.4 in the smaller adult females to 13.7 in the larger adult males)
in the subsimus group of large subspecies. The breadth of rostrum
in the fossil is 40.3 per cent of the length of the rostrum. In living
Cratogeomys castanops (both the large and small subspecies groups,
and including both females and males) the breadth of rostrum
amounts to between 44.0 and 51.4 per cent of its length. The
rostrum in Cratogeomys perotensis (and in other species of the
merriami group) is relatively much broader than in Cratogeomys
castanops. Even though the rostrum of the fossil is narrower than
in Recent species of Cratogeomys, the ventral border in the area of
the palatine slits is more heavily constructed than in any of the
living species, and it is nearly parallel-sided rather than tapered
toward the midline anteriorly. At the lateral edge of the enamel
plate of the incisors there is a distinct shelf, a characteristic of the
merriami group of species and a feature not well developed in
Cratogeomys castanops.

I hestitate to refer this fragment to any of the living species,
although I would judge it to represent a form closer to the species
castanops than to the merriami group (C. perotensis). The rostrum
may represent, and probably does, an undescribed and extinct
species of Cratogeomys, but in my opinion it should not be given
formal taxonomic status until more adequate material is available.

If the fossil is actually Cratogeomys castanops, and if the fragment
is from an earlier deposit in the cave than is the material here
assigned to Cratogeomys castanops, the fossil stock could be ancestral
to the group of small subspecies provided there had been
a trend in evolution toward smaller size. Another possibility is
that a shift in geographic range of the kinds of Cratogeomys that
lived in the vicinity of the cave has occurred, and that the fossil
represents an evolutionary line with no close relationship to Recent
species and now is extinct. Additional material is needed before
the history of these species can be reconstructed with validity.

[Pg 545]

Description of Holotype.—Differs from any known living species
of Heterogeomys, by the significantly heavier and deeper ramus
(see Table 1 and Fig. 1). The holotype is compared with the
largest adult male of Heterogeomys hispidus (H. torridus is smaller
than hispidus) available to me in Table 1. Relative to the length
of the ramus (measured from the anterior mental foramen to the
posterior margin of the capsule that surrounds the root of the lower
incisor), the depth of the ramus anterior to the molariform tooth-row
is 33.0 per cent in H. onerosus compared with 27.3 per cent in
H. hispidus. If the fossil ramus is that of a female (females are
significantly smaller than males in Heterogeomys) then the differences
would be greater than recorded.

The angle between the anterior border of the coronoid process
and the dorsal border of the ramus of the mandible is more acute,
and the posteroventral margin of the ramus is more nearly straight,
in onerosus than in hispidus. The molariform tooth-row in onerosus
is only slightly longer (13.9 in contrast to 13.5) than in hispidus
and torridus. The ventral border of the massenteric ridge is weakly
developed in onerosus and hardly discernable whereas in the living
species of Heterogeomys the massenteric ridge is strongly developed
posteriorly forming a noticeable prominence.

Description of Paratypes.—The fossils are referable to the genus
Heterogeomys on the basis of the short lateral angular processes of
the lower jaw and on the basis of the associated upper incisors,
which have a single distinct sulcus that lies toward the inner margin
of each tooth. The isolated lower premolar that is referred to the
new species is as large as that of the holotype and has the enamel
pattern of Heterogeomys.[Pg 546]

One jaw fragment, L.A.C.M. (C.I.T.) No. 2368, is smaller
than the others and probably is from a young individual. Two
others L.A.C.M. (C.I.T.) No. 2384 and one unnumbered, are
smaller than the holotype, and possibly are the remains of females;
however, they have the same characteristic shape as the holotype.
Nevertheless, the two rami mentioned above are significantly larger
than in adult males of modern Heterogeomys and are especially
larger than in females. Another jaw fragment, L.A.C.M. (C.I.T.)[Pg 547]
No. 2385, is seemingly as large as, or perhaps larger than, the holotype,
although the posterior part of the ramus behind the alveolus
of m2 is missing. An additional unnumbered ramus is of somewhat
lighter construction than the holotype, but is important since it
bears not only the incisor and p4 but also the first two lower molars.
The only other material referable to Heterogeomys onerosus is a
fragmentary and isolated lower molar tooth that has a single posterior
enamel blade, a feature characteristic of a number of Recent
genera of pocket gophers, and some limb bones which are slightly
larger than corresponding elements in Recent species of Heterogeomys.

Remarks.—Pocket gophers do not inhabit caves; therefore gophers
were brought into the cavern probably by birds of prey, the remains
of which were common in the deposits (Miller, 1943:152-156), or
conceivably by carnivorous mammals. Since most of the raptorial
predators that would prey on pocket gophers do not have a wide
hunting territory, it is likely that the gophers were taken within
a short distance of the cave. The presence of the genus Heterogeomys
in the deposits strongly suggests a tropical situation in the
vicinity of the cave when these gophers were taken, because the
distribution of this genus today is entirely within the Tropical
Life-zone.

Since the presumably early time when tropical conditions, or more
nearly tropical conditions, prevailed at San Josecito Cave, climatic
shifts account for a humid boreal environment there and its associated
fauna. Findley (lit. cit.:635-636) reports from San Josecito
the remains of the boreal shrew Sorex cinereus that today occurs no
nearer than 800 miles to the northward in the mountains of north-central
New Mexico. As he points out, that species requires hydric
communities of cool climates, and in the Wisconsin Glacial age such
climates probably prevailed in the high mountainous region where
San Josecito is located. Since the time when a more mesic boreal
environment occurred at San Josecito, climatic shifts have favored
more xeric conditions as are found in the vicinity of the cave today.
The more arid environments would support the occurrence of Cratogeomys
and Thomomys; however the ecological affinities of the
fragment here referred to Cratogeomys sp. are unknown.

The more nearly tropical environment there could have occurred
either during a Wisconsin interglacial period or during the Sangamon
Interglacial age. Heterogeomys onerosus perhaps lived near
the cave during an interglacial period; since then it became extinct[Pg 548]
or evolved into the Recent species Heterogeomys hispidus. Heterogeomys
has not previously been recorded from Pleistocene or
earlier deposits.

Baker, R. H.

Cushing, J. E., Jr.

Findley, J. S.

Handley, C. O., Jr.

Hooper, E. T.

Jakway, G. E.

Jones, J. K., Jr.

Miller, L.

Russell, R. J., and Baker, R. H.

Transmitted October 28, 1959.

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