By
JAMES S. FINDLEY
Bones of a large number of vertebrates of Pleistocene age have
been removed from San Josecito Cave near Aramberri, Nuevo
León, México. These bones have been reported upon in part by
Stock (1942) and Cushing (1945). A part of this material, on loan
to the University of Kansas from the California Institute of Technology,
contains 26 rami and one rostrum of soricid insectivores.
Nothing seems to be known of the Pleistocene Soricidae of México.
The workers cited do not mention them and no shrews are listed
by Maldonado-Koerdell (1948) in his catalog of the Quaternary
mammals of México. Comparison of these specimens with pertinent
Recent material from México, the United States, and Canada
leads me to the conclusion that they represent two genera and at
least three species. The material examined is described below.
One right ramus, bearing all three molars but lacking the other
teeth and the tip of the coronoid process, needs close comparison
only with certain of the smaller North American species of Sorex.
From S. merriami of southeastern Wyoming, it differs in having a
shorter, much shallower dentary, a shorter molar row, and a lower
coronoid. In every particular it is identical with Sorex cinereus.
Sorex cinereus from northern British Columbia and the specimen
from Nuevo León differ from Sorex saussurei, S. obscurus, and
S. vagrans in the ratio of the height of the coronoid to the length
of the dentary. This ratio averages 49.6% in S. cinereus and 53.0%
or more (up to 60.0%) in the other species. Microsorex hoyi differs
from S. cinereus and from the specimen in question in deeper and
shorter dentary, more robust condyle, dentary less bowed dorsally,
molars shorter in anteroposterior diameter and higher in proportion
to this dimension.
This record, as far as I can determine, constitutes a southward
extension of the known Pleistocene or Recent range of this species
of approximately 800 miles. The nearest known occurrence of
S. cinereus in Recent times is in the mountains of north-central
New Mexico. The species now has an extensive range in boreal
North America and prefers mesic and hydric communities from
which it rarely wanders. I know of no instance of the occurrence
of the cinereous shrew in desert areas such as there are between
many of the mountain ranges of southern New Mexico, Coahuila,
and Nuevo León. Therefore, unless the habitat preferences of the
species have changed since Pleistocene times, this find constitutes
additional evidence that more humid conditions at one time prevailed
in the regions mentioned.
Fragments of three other specimens of Sorex occur in the collection.
One of these is a right ramus, C. I. T. No. 3943, and is complete
except for the canine. The other two bear no numbers and
I have designated them "A" and "B." "A" is a left ramus with the
dentary broken off anterior to the canine and bears p4 and the
canine. "B" is a right ramus bearing m2 and the roots of m3 and
is broken off at the middle of the alveolus of m1. Each specimen
has certain peculiarities but they resemble one another so closely
that I regard all three as of the same species. The teeth, where
comparable, are of essentially the same size and configuration. The
horizontal rami of the dentaries are the same. The fossils differ,
however, in the configuration of the coronoid process. In No. 3943
the coronoid is robust and inclined anteriorly with respect to a
line drawn perpendicular to the dentary. The posterointernal ramal
fossa (see Hibbard, 1953) is deeply excavated with a distinct
superior border approximately halfway between its inferior border
and the top of the coronoid. In addition to the mandibular foramen
there is a small foramen immediately posterior to it opening into
the posterointernal ramal fossa. I shall refer to this as the post-mandibular
foramen. The tip of the coronoid is broad, not tapering,
and quadrate, and its entire superior border is inclined rather
sharply medially. Specimen "B" differs from No. 3943 in that the
posterointernal ramal fossa extends nearly to the tip of the coronoid,
which is narrower toward the tip and somewhat tapered dorsally.
The post-mandibular foramen is large and the opening of the
mandibular canal is within the posterointernal ramal fossa. In
addition the coronoid does not incline anteriorly. Specimen "A"
is intermediate between No. 3943 and "B" in the characters mentioned
and differs from both in that the post-mandibular foramen
is widely separated from the mandibular foramen.
Comparison of the Pleistocene specimens with specimens of Recent
species of North American Sorex reveals that the presence or
absence of the post-mandibular foramen is almost constant in any
one species. In possessing this foramen the fossils differ from most
individuals of the species: Sorex cinereus, S. pacificus, S. milleri,
S. vagrans, S. obscurus, S. ornatus, S. fumeus, S. palustris, S. bendirii,
and S. veraepacis. The fossils differ from all these species in other
characters as well; consequently detailed comparisons with them
need not be made here. Species which possess the post-mandibular
foramen include Sorex saussurei, S. merriami, S. trowbridgii,
S. arcticus, S. tundrensis, and S. sclateri. Sorex merriami differs in
smaller size, smaller and weaker dentition, relatively higher coronoid,
and relatively deeper and shorter dentary. Sorex trowbridgii
is similar to the fossils and to S. saussurei. Differences between
the jaws of S. trowbridgii and S. saussurei seem to me to be differences
of size only. Sorex sclateri is larger than the fossils and m2
is longer in relation to m1, being almost the same size as m1. In
the fossils m2 is noticeably shorter than m1, owing to close appression
of the hypoconid and protoconid and in general to a smaller
talonid area. Sorex arcticus differs in larger incisor and p4. Sorex
tundrensis differs in relatively narrower molars. I have compared
the fossils also with the Pliocene and Pleistocene Sorex taylori
Hibbard, and find that the fossils are larger and have larger teeth
and a much wider separation of the protoconid and metaconid. I
can find no significant way in which the fossils differ from S. saussurei.
This of course implies similarity to S. trowbridgii. Since
S. saussurei is a widespread species in México today and since it
occurs in the vicinity of the San Josecito area the specimens under
discussion are referred to this species.
The San Josecito collection contains 22 rami of a species of
Cryptotis. Many are nearly complete although none possesses the
incisor. In addition there is a rostrum that on the right side bears
the last two unicuspids, P4, M1, and M2. I have compared these
fossils with specimens of the following species of Cryptotis:
C. mexicana, C. magna, C. nelsoni, C. thomasi, C. alticola, C. parva,
C. orophila, C. pergracilis, C. guerrerensis, C. obscura, C. mera,
C. soricina, C. fossor, C. goodwini, C. griseoventris, C. meridensis,
C. mayensis, and C. micrura. The four species first mentioned and
the fossils seem to fall into one group. The remaining species fall
into another group characterized by a smaller occlusal area of the
talonid on all three molar teeth with respect to the trigonid, and
especially by the smaller and weaker talonid of m3 which possesses
only one bladelike cusp, the hypoconid. In the first four species
the talonids are larger than in the other species when compared
to the trigonids, and the talonid of m3 possesses a well developed
hypoconid and entoconid with a distinct basin between them. The
rami of San Josecito specimens closely resemble those of C. mexicana
in both size and qualitative characters. The rostrum mentioned
above differs from those of C. mexicana in that the unicuspids
are larger, especially the posteriormost one. Cryptotis thomasi and
C. magna are eliminated from consideration here on geographical
grounds. Little difference may be seen between the rami of
C. mexicana mexicana from Veracruz and C. nelsoni. The fossils
are referred to the former species since it has a rather wide distribution
in México in contrast to C. nelsoni which is restricted to
Volcán de Tuxtla, Veracruz. The northernmost Recent occurrence
of C. mexicana known to me is from Las Vigas, Veracruz. As far
as I know the species has not previously been recorded from the
Pleistocene.
Stirton (1930:225), in summarizing the group characters of Recent
Soricidae, listed the bicuspid talonid of m3 as one of the characters
of the "Blarina group," which includes Neomys, Soriculus,
Notiosorex, Chimarrogale, Cryptotis, and Blarina. That this character
does not obtain universally within the group is demonstrated
by the unicuspid structure of the talonid of m3 of the majority of
the species of Mexican Cryptotis.
I am grateful to Drs. David E. Johnson and Henry W. Setzer of the United
States National Museum, and to Dr. John Aldrich and Miss Viola S. Schantz
of the United States Fish and Wildlife Service for permitting me to examine
specimens in their care. Also I am obliged to Professor E. Raymond Hall for
permission to study the specimens from San Josecito Cave. The late Professor
Chester Stock intrusted the specimens to Professor Hall for study and description.