Part 4

The genus _Pappogeomys_ is not known from Pleistocene deposits older than the Wisconsin glaciation, but a pre-Pleistocene occurrence in the Benson beds of Arizona (see discussion of the Pliocene above) shows that _Pappogeomys_ had been differentiated by late Pliocene time. The absence of _Pappogeomys_, beginning in the early Pleistocene and continuing well into the late Pleistocene, is attributed to the southern distribution of the genus, where its range probably was centered on the Central Plateau of México. The paucity of early and middle Pleistocene deposits from this critical region prevents any definite statements about phyletic development within the genus. All of the late Pleistocene records pertain to the subgenus _Cratogeomys_ (long in use as a generic name but in the present paper reduced to subgeneric rank in the genus _Pappogeomys_). Schultz and Howard (1935:280) found _Cratogeomys_ [= _Pappogeomys_] _castanops_ in Burnett Cave in the Guadalupe Mountains of south-central New Mexico. The Burnett deposits are probably late Wisconsin (see Schultz and Tanner, 1957:75, for discussion of the age of these deposits based on carbon-14 tests). These writers (_loc. cit._) also referred the mandible of a small pocket gopher to the genus _Pappogeomys_ [= subgenus _Pappogeomys_]. However, neither genera nor subgenera of the tribe Geomyini can be distinguished on the basis of their inferior dentitions. Judging from the distribution of the modern geomyines, it seems unlikely that the subgenus _Pappogeomys_ has occurred beyond its present range in the late Pleistocene; therefore the small mandible is most likely that of a young individual of _Pappogeomys castanops_. Russell (1960:543) referred specimens collected at San Josecito Cave in Nuevo León, México, to the group of small subspecies _Cratogeomys_ [= _Pappogeomys_] _castanops_. Also, Russell (_loc. cit._) identified a rostral fragment as of the genus _Cratogeomys_ [= subgenus _Cratogeomys_] although the fragment had a combination of features different than in any named species of the genus; he did not name the fragment as a new species, preferring to wait for additional material that could clarify its taxonomic relationships.

Hibbard (1955a:52-53) identified _Cratogeomys_ [= _Pappogeomys_] _tylorhinus_ from the Becerra Superior deposits in the valley of Tequixquic in the northern part of the state of México. The Wisconsin age of these beds suggests an earlier Pleistocene derivation of the _gymnurus_-group of species.

Several specimens of the subgenus _Cratogeomys_ have been reported 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.