from beds of latest Wisconsin (certainly after the glacial maximum)
or post-Wisconsin age. Gilmore (1947:158) found fossil remains of
_Cratogeomys_ [= _Pappogeomys_] _castanops_ commonly in Quaternary
cave deposits on the mountain slopes in the vicinity of Cuatro
Ciénegas, in central Coahuila. These deposits actually may be of
post-Wisconsin origin (see discussion above). Alvarez (1964:8)
obtained fragments of _Cratogeomys_ [= _Pappogeomys_] _tylorhinus_
from sub-Recent deposits of Capa III in the Cueva La Nopalera in
southwestern Hidalgo, México. _Pappogeomys merriami_ lives in the
area today. Mayer-Oakes (1959:373) reported remains of _Cratogeomys_
[= _Pappogeomys_] _merriami_ from levels eight and eleven of the
excavations at El Risco II, in the northern part of Mexico City. The
ages of these deposits are unknown to me, but they probably are no
older than late Wisconsin with most of the beds dating from the
post-Wisconsin.
_Orthogeomys_
This genus is not known from the Pleistocene, except for its
occurrence in the San Josecito cave deposits of southwestern Nuevo
León, México (Russell, 1960:544). Although _Orthogeomys_ does not
occur in the immediate vicinity of the cave at the present time, the
northern limits of its range is nearby in southern Tamaulipas. The
_Orthogeomys_ from San Josecito Cave differs from living species,
and has been named _Heterogeomys_ [= _Orthogeomys_] _onerosus_
Russell (_loc. cit._), and is evidently referable to the subgenus
_Heterogeomys_. As mentioned before, the San Josecito Cave local
fauna represents deposits of Wisconsin glaciation.
HISTORY OF CLASSIFICATION
The account of the Tucan or Indian mole by Hernandez (sometimes listed
as Fernandez) in 1651 probably is the earliest published one of a
geomyid (see Merriam, 1895:201; Coues, 1877:607-608). Linnaeus in 1758
did not mention geomyids. In 1772, Kerr described Hernandez's Tucan
under the name _Sorex mexicana_ on the basis of Hernandez's account
without having seen any specimens. Lichtenstein in 1827 applied the
technical name _Ascomys mexicana_ to three specimens collected by
Deppe from unknown localities on the tableland of México. Merriam
(_loc. cit._) pointed out that the name _mexicanus_ of Lichtenstein in
1827 is a _nomen nudum_, and that it is preoccupied by _mexicanus_
used by Kerr in 1792. The latter can not be technically identified
with any particular species of geomyid.
Bartram in 1791 wrote of the pocket gopher of Florida, without
formally describing it. The first available technical name is _Mus
bursarius_ of Shaw in 1800. Rafinesque in 1817 proposed the first
generic names for the geomyids when he described _Geomys_ and
_Diplostoma_. In 1839, Waterhouse referred the genus _Geomys_ to his
family Arvicolidae, considered by him to be a subgroup of muroids. In
1841, he suggested that _Geomys_ was related to _Bathyergus_ and
_Spalax_. Waterhouse in 1848 (p. 8) treated the pocket gophers as a
subgroup of rodents under the group name Saccomyina, in which he
included the genera _Heteromys_, _Saccomys_, _Perognathus_, and
_Dipodomys_. Hence, Waterhouse was the first to recognize the
relationship between the heteromyids and geomyids. In the next year
Gervais erected the family Pseudostomidae for a group of specialized
squirrels to include _Geomys_ and _Thomomys_ and the same genera (at
least in part) of heteromyids that Waterhouse classified in the
"family" Saccomyina.
In 1839 the name _Thomomys_ was proposed by Maximilian (Wied-Neuwied).
All of the generic names previously proposed for pocket gophers were
considered by subsequent authors to be synonyms of _Geomys_.
A third family name, Sciurospalacoides, was proposed by Brandt
(1855:188) who referred _Geomys_ and _Thomomys_ to that family. He
placed his new family phylogenetically between the family Sciuridae
and the family Spalacoides (a group in which Brandt included the
genera _Spalax_, _Sipheus_, and _Ellobius_). Brandt took exception
to the classification of Waterhouse (1848), who united the geomyids
and heteromyids in one family. Brandt placed the heteromyid genera
in other groups: _Perognathus_ in the Muridae, and _Macrocolus_
[= _Dipodomys_] in the Macrolini, a subfamily of the family Dipodoides.
Modern classification of the pocket gophers begins with Baird in 1858.
The important classifications are summarized in Table 1; a few that do
not depart essentially from those listed have been omitted owing to
limited space for the tabular arrangement, but are discussed in the
following account.
Baird probably was strongly influenced by the arrangement proposed by
Waterhouse in 1848, but was opposed to separating geomyids from
heteromyids as was done by Brandt. Baird was convinced of the close
relationship of the geomyids and heteromyids, and referred both groups
to one family, the Saccomyidae, as Waterhouse had done earlier. In
order to recognize the morphological specializations he used two
subfamilies, Geomyinae and the Saccomyinae. In the 20 years that
followed, some authors followed Brandt and others followed Baird.
Gill, in 1872 (p. 71), proposed a classification essentially like
Baird's of 1858, but Gill raised Baird's subfamilies to the rank
of family (see Table 1). In referring all pocket gophers to the
Geomyidae, Gill used that name as a family term for the first time.
Also he established the superfamily Saccomyoidea to include his two
families, Geomyidae and Saccomyidae; therefore, the Saccomyoidea was
equivalent to the group Saccomyina of Waterhouse (1848) and the
Saccomyidae of Baird (1858). Coues (1877), in his classic monograph of
the Geomyidae followed the arrangement proposed by Gill in treating
the pocket gophers as a family. Alston in 1876 proposed another
classification based on Baird (1858), with two subfamilies, the
Geomyinae and the Heteromyinae, united together in the family
Geomyidae; thus, he recognized that the genus _Saccomys_ Frédéric
Cuvier, 1823, was a synonym of _Heteromys_ Desmarest, 1817, as had
been pointed out by Gray (1868:201) and Peters (1874:356). Coues
(1877:487-490) acknowledged the invalidity of the genus _Saccomys_,
but refused to give up the name in supergeneric classification. Winge,
first in 1887 and subsequently in 1924, classified the geomyids and
heteromyids together in the family Saccomyidae as did Baird in 1858,
and like Coues, Winge too ignored the synonymy of _Saccomys_ with
_Heteromys_ and insisted on retaining the technical terms Saccomyidae
and Saccomyini.
Up to the time of Merriam's classic revision of the Recent Geomyidae
in 1895 all the known species of living pocket gophers were referred
to two genera, _Geomys_ and _Thomomys_. Merriam described much new
material, especially from México and Central America, and proposed
seven new genera (see Table 1). His complete and detailed study of the
dentitions and osteology of the skull remains today as the definitive
work on this subject, and is the point where most studies of the
Geomyidae must begin. His treatment of the Recent genera survived for
52 years without change until Hooper (1946:397) arranged _Platygeomys_
as a synonym of _Cratogeomys_. However, Merriam's genera have been
recognized in all subsequent classifications except for the current
review (see Table 1).
Cope described the first known fossil geomyids in 1878, and published
an excellent review of the two genera, _Pleurolicus_ and _Entoptycus_,
in 1884 (pp. 855-870, pl. 64, figs. 1-9). Both genera were recovered
from the John Day Miocene deposits of Oregon. Cope did not propose a
new systematic arrangement of these geomyids, but referred them to the
family Saccomyidae and mentioned that the Saccomyidae was equivalent
to the family Geomyidae of Alston. Winge, in 1887, followed Cope in
referring _Pleurolicus_ and _Entoptycus_ to the Saccomyidae along with
the living genera _Thomomys_ and _Geomys_. Miller and Gidley (1918),
in their synopsis of the supergeneric groups of rodents, proposed a
new subfamily, Entoptychinae, to include the divergent Miocene pocket
gophers. Miller and Gidley also revived the old subfamily Geomyinae of
Baird (1858), but restricted its application to the modern pocket
gophers and their immediate ancestors. In 1936, A. E. Wood revised the
taxa of the subfamily Entoptychinae, and described the first Miocene
genus, _Dikkomys_, of the Geomyinae. He followed the supergeneric
classification of Miller and Gidley (1918).
The recent classifications of Simpson (1945) and Wood (1955) have
combined the classifications of Merriam (1895) and Wood (1936). Wood
(1955) brought up to date the list of genera, including those that
were described after the publication of Simpson's classification
(1945). In Table 1, the list of genera is principally from Simpson
(1945) but generic names used by Wood (1955) are included. This is the
currently accepted classification.
The new classification proposed in this paper (see Table 1) includes
three tribes proposed as vertical units; they are intended to stress
the phyletic trends in the known evolutionary sequences by placing
immediate ancestors together with their descendants.
_Pliogeomys_ is placed in the same tribe (Geomyini) as _Zygogeomys_,
_Geomys_, _Orthogeomys_, and _Pappogeomys_. That tribe includes the
most specialized Geomyinae. _Zygogeomys_, _Geomys_, _Orthogeomys_, and
_Pappogeomys_ are lineages resulting from a Pleistocene radiation in
which all the lineages diverged from a common Pliocene ancestor. The
radiation of the Geomyini was well under way by the close of the late
Pliocene. Although _Pliogeomys_ may not be the actual ancestor, it
closely resembles the primitive morphotype.
TABLE 1.--History of the classification of the Superfamily Geomyoidea
===============+==============+==================+================
Baird 1858 | Gill 1872 | Winge 1887 | Merriam 1895
| Coues 1877 | and 1924 | Ellerman 1940
---------------+--------------+------------------+----------------
Family | Family | Family | Family
Saccomyidae | Geomyidae | Saccomyidae | Geomyidae
---------------+--------------+------------------+----------------
Subfamily | | "Group" |
Geomyinae | | Geomyini |
-- -- -- -- -- +-- -- -- -- --+-- -- -- -- -- -- +-- -- -- -- -- -
| | |
| | |
| | |
| | |
| | |
| | |
| | |
| | |
| | |
| | |
_Thomomys_ | _Thomomys_ | _Thomomys_ | _Thomomys_
| | |
| | |
| | |
| | |
| | |
| | | _Zygogeomys_
| | |
| | |
_Geomys_ | _Geomys_ | _Geomys_ | _Geomys_
| | |
| | | _Orthogeomys_
| | | _Heterogeomys_
| | | _Macrogeomys_
| | |
| | | _Pappogeomys_
| | | _Cratogeomys_
| | | _Platygeomys_
-- -- -- -- -- +-- -- -- -- --+-- -- -- -- -- -- +-- -- -- -- -- -
| | |
| | |
| | |
| | *_Pleurolicus_ |
| | |
| | |
| | *_Entoptychus_ |
---------------+--------------+------------------+----------------
| | |
| | |
| | |
| | "Group" |
| | Gymnoptychine** |
| | _Gymnoptychus_ |
---------------+--------------+------------------+----------------
Subfamily | Family | "Group" |
Saccomyinae | Saccomyidae | Saccomyini |
-------------+-------------+------------------+----------------
=====================+=====================+===================
Wood 1935 | Simpson 1945 | Names used in
Wood 1936 | Wood 1955 | present paper
---------------------+---------------------+-------------------
Family | Family | Family
Geomyidae | Geomyidae | Geomyidae
---------------------+---------------------+-------------------
Subfamily | Subfamily | Subfamily
Geomyinae | Geomyinae | Geomyinae
-- -- -- -- -- -- -- +-- -- -- -- -- -- -- +-- -- -- -- -- -- -
| | Tribe
| | Dikkomyini
| |
*_Dikkomys_ | *_Dikkomys_ | *_Dikkomys_
| *_Pliosaccomys_ | *_Pliosaccomys_
| |
| | Tribe
| | Thomomyini
| |
*_Pleisothomomys_ | *_Pleisothomomys_ | }
_Thomomys_ | _Thomomys_ | } _Thomomys_
| |
| | Tribe
| | Geomyini
| |
| *_Pliogeomys_ | *_Pliogeomys_
_Zygogeomys_ | _Zygogeomys_ | }
| *_Nerterogeomys_ | } _Zygogeomys_
| |
_Geomys_ | _Geomys_ | }
| *_Parageomys_ | } _Geomys_
_Orthogeomys_ | _Orthogeomys_ | }
_Heterogeomys_ | _Heterogeomys_ | } _Orthogeomys_
_Macrogeomys_ | _Macrogeomys_ | }
| |
_Pappogeomys_ | _Pappogeomys_ | }
_Cratogeomys_ | _Cratogeomys_ | } _Pappogeomys_
_Platygeomys_ | _Platygeomys_ | }
-- -- -- -- -- -- -- +-- -- -- -- -- -- -- +-- -- -- -- -- -- -
Subfamily | Subfamily | Subfamily
Entoptychinae | Entoptychinae | Entoptychinae
| |
*_Pleurolicus_ | *_Pleurolicus_ | *_Pleurolicus_
*_Gregorymys_ | *_Gregorymys_ | *_Gregorymys_
*_Grangerimus_ | *_Grangerimus_ | *_Grangerimus_
*_Entoptychus_ | *_Entoptychus_ | *_Entoptychus_
---------------------+---------------------+-------------------
| Geomyidae | Geomyidae
| _incertae sedis_ | _incertae sedis_
| |
| |
*_Gidleumys_ | *_Diplolophus_ | *_Diplolophus_
| *_Griphomys_ | *_Griphomys_
---------------------+---------------------+-------------------
Family | Family | Family
Heteromyidae | Heteromyidae | Heteromyidae
---------------------+---------------------+-------------------
* Denotes extinct genera.
** Winge included in his family Saccomyidae the "group"
Gymnoptychine and the contained genus _Gymnoptychus_ Cope, 1873,
which genus currently is placed in the family Eomyidae. The type
of _Gymnoptychus_ Cope, 1873, is synonymous with _Ischyromys_
Leidy, 1856, and the valid name for the genus is _Adjidaumo_
Hay, 1899.
_Pliosaccomys_, on the other hand, represents the terminal stages of a
long trend that began with the _Dikkomys_-like Geomyinae of the early
Miocene. In this lineage, the rate of evolution in the dentition and
the skull was slow; therefore, the differences between early Miocene
(_Dikkomys_) and middle Pliocene (_Pliosaccomys_) are not great and
the two are united into the tribe Dikkomyini. The Dikkomyini is the
ancestral geomyinen trunk from which the modern groups have diverged.
The Pliocene ancestor of _Thomomys_ is unknown but probably resembled
_Pliosaccomys_, with which it may have been a contemporary. _Thomomys_
is the least specialized of the modern Geomyinae, and, consequently,
shows the most resemblance to the ancestral tribe. The specializations
of _Thomomys_, however, clearly preclude its reference to the tribe
Dikkomyini; therefore, it is set apart in the monotypic tribe
Thomomyini. That tribe has not undergone an adaptive radiation
comparable to that of the tribe Geomyini or that of the Entoptychinae
in the early Miocene. Here, for the first time, _Thomomys_ is set
apart in classification from the other living pocket gophers.
Merriam's genera _Orthogeomys_, _Heterogeomys_, and _Macrogeomys_ are
closely related. Each of these taxa is retained as a subgenus of a
single genus, _Orthogeomys_. Some species of _Macrogeomys_ seem to be
more closely allied to the subgenus _Orthogeomys_ and others to the
subgenus _Heterogeomys_. A revision of the genus is needed; it might
show that the currently recognized subgenera are artificial, and that
a different arrangement of the species would more clearly express
their evolutionary relationships. The subgenus _Heterogeomys_ seems to
be the most nearly uniform of the subgenera, and it is the least
specialized. Radiation within the genus may have begun relatively
recently, but the many special adaptations for tropical environments
suggest that the genus has been in the Neotropical Zone a long time.
Therefore, discovery of an early dichotomy from the common ancestral
stock of the tribe would come as no surprise.
_Nerterogeomys_ Gazin here is arranged as a junior synonym of
_Zygogeomys_. Both are less specialized than any of the other
Geomyini, except _Pliogeomys_. The single living species (_Zygogeomys
tricopus_) is obviously a relic. Its range is small. The two
subspecies differ only in minor features. The living species does
have a few unique characteristics, only to be expected in the
surviving species of a long phyletic lineage. Some of these are
specializations. Otherwise, _Zygogeomys_ and _Nerterogeomys_ are
closely related and the latter is best placed as a synonym of the
former. Both are admittedly closely related to _Geomys_. _Zygogeomys_
and _Geomys_ share several characters, particularly primitive ones;
there is considerable parallelism, especially marked in Irvingtonian
species of _Geomys_. Nevertheless, _Geomys_ is more specialized,
particularly in the dentition, and it has developed some
_Pappogeomys_-like specializations. _Zygogeomys_ has retained more of
the primitive characters of the tribe. A strong case could be made for
recognizing only one genus, _Geomys_, containing _Zygogeomys_ as one
of two subgenera. Nevertheless, the characters separating _Zygogeomys_
and _Geomys_ are of considerable importance and I consider the two
kinds to be distinct genera.
The species of _Geomys_, both living and extinct, form a distinct and
well-marked group. The genus is less primitive in most respects than
_Zygogeomys_ and _Orthogeomys_ and it is less specialized than
_Pappogeomys_, excluding the ancestral stock (subgenus _Pappogeomys_).
Some specimens of species of Irvingtonian age (_Geomys tobinensis_ and
_Geomys garbanii_, especially the former) retain primitive enamel
plates as does _Zygogeomys_; but this is true of only a small
percentage of the individuals. Also the adult dental pattern developed
somewhat later in ontogeny in these middle Pleistocene species of
_Geomys_ than in either Recent or late Pliocene and early Pleistocene
representatives (_Geomys paenebursarius_, _Geomys quinni_) of the
genus. Whether these features represent a stage in the evolution of
the late Pleistocene and Recent species or a terminal stage in members
of a sterile and primitive branch of the main line of evolution of
_Geomys_ is uncertain. At present I favor the latter explanation, and
view _G. paenebursarius_ and _G. quinni_ as early progressive species
that evolved dental specializations that were maintained in the main
line of phylogeny.
Hibbard proposed the generic name _Parageomys_ (1944:55), but later
regarded it as a subgenus of _Geomys_ (1956:182) that includes those
species retaining continuous enamel bands until relatively late in
ontogeny; no other differences have been noted. When the early
phylogeny of _Geomys_ is better understood, _Parageomys_ may serve as
a subgeneric taxon in which the primitive species of _Geomys_ can be
grouped, but as of now _Parageomys_ is arranged as a synonym of
_Geomys_.
_Pappogeomys_ and _Cratogeomys_ also form a natural group. Their close
relationship is best reflected in formal taxonomy by including them in
the same genus. Their dissimilarities are of the sort that separate a
primitive ancestral lineage from a divergent and progressively more
specialized assemblage. The fossil record is inadequate, and I
can only speculate that _Cratogeomys_ diverged from primitive
_Pappogeomys_-stock in the earlier Pleistocene, at least before the
end of the Irvingtonian. _Cratogeomys_ probably originated on the
Mexican Plateau and probably underwent its subsequent evolution there.
The living species of the subgenus _Pappogeomys_ are evidently relics
of the ancestral stock of the genus. Hooper (1946:397), I think
correctly, considered _Platygeomys_ as congeneric with _Cratogeomys_,
although the highest degree of specialization of the genus is attained
in those species formerly classed in the genus _Platygeomys_. Even so,
in my opinion, the differences are insufficient to warrant even
subgeneric recognition.
CLASSIFICATION
Family GEOMYIDAE Gill, 1872
Rodents of the superfamily Geomyoidea specialized for completely
fossorial life (early Pliocene to Recent); specialized earlier (late?
Oligocene and early Miocene) for semi-fossorial habits; body thickset,
fusiform without apparent neck (in modern geomyids); legs short;
forelegs especially stout; eyes and ears small (pinna reduced to
inconspicuous crest concealed beneath pelage); tail tactile, shorter
than head and body; lips closing behind incisors; cheek pouches
external, fur-lined; baculum rodlike, arched, having expanded
quadriform platelike base; pelage long, soft without underfur,
covering body in thick coat (in some species of _Orthogeomys_ scant,
harsh or scattered bristles); color varying from pale tints of buffy
(almost white) to metallic black.
Skull thick-walled, massive, angular, relatively broad, and flattened;
distinctly murine form, but having zygomasseteric structure of
advanced sciuromorphs, including small infraorbital canal (that
transmits no part of masseter muscle) and well-developed, broad
zygomatic plate; zygomata massive and widely flaring, jugals stout;
rostrum robust, relatively broad and deep, and without evidence of
transverse canal (as in Heteromyidae); anterior projection of nasals
only slightly exceeding that of upper incisors; interorbital region
usually constricted, narrower than rostrum; anterior opening of
infraorbital canal far forward on side of rostrum, about half
way between zygomatic plate and upper incisor and just behind
premaxillary-maxillary suture, its opening countersunk in oblique
sulcus (for protection from muscle contraction); postorbital process
lacking, except for rudimentary knoblike projection in subgenus
_Macrogeomys_; palate relatively narrow, its deeply sculptured surface
sloping steeply downward posteriorly causing region supporting
maxillary tooth-row to be markedly depressed; palatine bone reduced,
forming, on two abruptly different levels, posterior margin of hard
palate behind tooth-rows; parietals compressed and narrow, and most of
cerebral cavity roofed by squamosals (in some species squamosals
overlap lateral parts of parietals); tympanic bullae completely
inferior in position and fully ossified, external meatus being
developed laterally as elongated tube; mastoid not inflated, but
broadly exposed at posterolateral margin of the skull; occiput large,
its surface usually rugose, and paroccipital processes large and
flangelike, at least in advanced groups (early Pliocene to Recent);
ramus relatively short and stout, having distinct crest and ridges
for muscle attachments; coronoid process well developed, erect;
articular condyle prominent; angular process prominent, reflected
laterally, and in modern groups lateral extension protruding from
posterior border of ramus nearly at right angle; capsule for root of
lower incisor, prominent between angular process and articular
condyle.