Part 7

The masseteric ridge of the mandible is well developed. In the late Pliocene species _Z. persimilis_ and _Z. minor_ the mental foramen is directly beneath the anterior extension of the masseteric ridge, but in the living species, _Z. trichopus_, the foramen lies well anterior to the ridge. The basitemporal fossa in the living species is well developed and deep; in the Pliocene species it is usually distinct but shallow (late Pliocene specimens of _Z. minor_).

_Referred species._--Three (two extinct and one living; the last has two subspecies):

*_Zygogeomys minor_ (Gidley), 1922. U. S. Geol. Surv. Prof. Paper, 131:123, December 26. Type from Benson local fauna (late Pliocene), Cochise County, Arizona; also known from the Rexroad local fauna, Meade County, Kansas.

*_Zygogeomys persimilis_ Hay, 1927. Carnegie Inst. Washington Publ., 136. Originally described by Gidley, 1922 (U. S. Geol. Surv. Prof. Papers, 131:123, December 26) as _Geomys parvidens_ which was preoccupied by _G. parvidens_ Brown, 1908. Type from Curtis Ranch local fauna (middle Pleistocene), Cochise County, Arizona.

_Zygogeomys trichopus trichopus_ Merriam, 1895. N. Amer. Fauna, 8:196, January 31. Type from Nahuatzen, Michoacán.

_Zygogeomys trichopus tarascensis_ Goldman, 1938. Proc. Biol. Soc. Washington, 51:211, December 23. Type from 6 mi. SE Pátzcuaro, 8,000 ft., Michoacán.

Genus =Geomys= Rafinesque

1817. _Geomys_ Rafinesque, Amer. Monthly Mag., 2(1):45, November.

1817. _Diplostoma_ Rafinesque, Amer. Monthly Mag., 2(1):44-45, November. Included species: _Diplostoma fusca_ Rafinesque [= _Mus bursarius_ Shaw] and _Diplostoma alba_ Rafinesque [= _Mus bursarius_ Shaw] from the Missouri River region.

1820. _Saccophorus_ Kuhl, Beitr. Zool. und Vergl. Anat., pp. 65, 66. Type: _Mus bursarius_ Shaw, from upper Mississippi Valley.

1823. _Pseudostoma_ Say, Long's Expd. Rocky Mts., I, pp. 406. Type: _Pseudostoma bursaria_ [= _Mus bursarius_ Shaw], from upper Mississippi Valley.

1825. _Ascomys_ Lichtenstein, Abh. K. Akad. Wiss. Berlin (1822), p. 20., fig. 2. Type: _Ascomys canadensis_ Lichtenstein [= _Mus bursarius_ Say], probably from upper Mississippi Valley.

1944. _Parageomys_ Hibbard, Bull. Geol. Soc. Amer., 55:735, June. Type: _Parageomys tobinensis_ Hibbard, from Pleistocene, Cudahy (Tobin) local fauna, Russell Co., Kansas.

_Type._--_Geomys pinetis_ Rafinesque, 1817, restricted to Screven County, Georgia, in region of the pines.

_Chronologic range._--Late Pliocene faunas of Blancan age (Rexroad, Kansas, and Sand Draw, Nebraska, local faunas) to Recent. Reported from numerous Pleistocene deposits of all stratigraphic levels, especially from the Great Plains, where common today.

_Description and discussion._--Pocket gophers of this genus are medium-sized geomyids; none is so small as the average-sized _Thomomys_. The skull is generalized and lacks the dolichocephalic and platycephalic specializations seen in the genera _Orthogeomys_ and _Pappogeomys_, respectively. _Geomys_ closely resembles _Zygogeomys_, but retains fewer of the primitive characters of the ancestral stock. At the same time, _Geomys_ has several specializations. Even so, a considerable amount of parallelism is evident in the phyletic trends of the two genera.

The upper incisor of _Geomys_ is bisulcate as in _Pliogeomys_ and _Zygogeomys_; the deeper grove is medial and the shallower grove lies near the inner border of the tooth. The premolar, above and below, is bicolumnar; and two columns are joined at their mid-points (deep re-entrant angles separate the columns at the sides). A permanent enamel plate protects the anterior face of the anterior loph, and enamel bands outline each of the re-entrant folds. In p4 a complete enamel plate covers the posterior surface of the posterior loph. All of the enamel bands are interrupted by tracts of dentine, except in the initial stages of wear of the occlusal surface of the newly erupted tooth. For a short time in living _Geomys_, the enamel bands are continuous as observed in juveniles of _Geomys bursarius major_ (KU 5628, 8531, and 41540). But, the enamel cap is thin and the dentine tracts, which are high on the sides of the tooth, are soon revealed by a minimum of wear on the crown. Therefore, the adult, or final, pattern characterized by interrupted enamel plates emerges early in life and remains throughout the life of the individual. Evidence from fossil _Geomys_, especially from specimens from early and late Pleistocene deposits, suggests that the final adult pattern appears later, ontogenetically, than in Recent specimens. Some of the fossil premolars in initial stages of wear have continuous and uninterrupted bands of enamel. _Geomys quinni_ of the late Pliocene and early Pleistocene has the interrupted pattern seen in late Pleistocene and Recent _Geomys_. Also, in late Pliocene and early Pleistocene species, the re-entrant folds diverge laterally and form "open" angles. In later taxa (middle Pleistocene to Recent) the folds are compressed and parallel-sided, and the "open" folds are found only in the early stages of wear.

The posterior enamel plate of P4 disappears in the final stages of wear as the interrupted enamel pattern is formed. In the late Pleistocene and Recent _Geomys_, the loss of the posterior plate occurs early in life, usually in the first phases of wear on the occlusal surface of the newly erupted tooth, but in fossils of _Geomys_ of corresponding ontogenetic age from the early and middle Pleistocene, the posterior plate is retained in some individuals until a later phase of wear, thereby delaying the appearance of the final pattern. Indeed, in five or fewer per cent of the individuals (see Paulson, 1961:138-139; and White and Downs, 1961:18) a vestige of enamel is retained throughout life or at least until late in adulthood. In _Geomys tobinensis_, for example, a thin, but transversely complete, plate of enamel occurs all the way down to the base of the loph (Paulson, _loc. cit._) and would persist throughout life. In _Geomys garbanii_, a vestige on the lingual side of the posterior surface of a fully adult specimen was noted by White and Downs (_loc. cit._). Vestiges of the posterior plate occur less frequently in living geomyids. Paulson (_loc. cit._) found a posterior plate in one of 75 specimens of _Geomys bursarius dutcheri_. A young (suture present between exoccipitals and supraoccipital) female of _Geomys pinetis austrinus_ (KU 23358) has a vestige of the posterior plate on the lingual side of the tooth as White and Downs (_loc. cit._) observed in a specimen of _Geomys garbanii_. The enamel, I suspect, tends to be thicker on the lingual than on the labial side of the loph and extends farther down the lingual surface in some individuals; therefore, wear on the occlusal surface erodes it down to the dentine more rapidly on the labial than on the lingual side. The tendency of enamel to be retained is a primitive feature.

A lower molar of _Geomys_ is a single elliptical column, and enamel is restricted to the posterior surface as in _Zygogeomys_, _Orthogeomys_, and _Pappogeomys_. Paulson (_loc. cit._) found a thin enamel plate on the anterior surfaces of the lower molars in about five per cent of the individuals of _Geomys tobinensis_ from the Cudahy local fauna (middle Pleistocene, deposits of the late Kansan glaciation). An anterior plate is unknown in other members of the tribe Geomyini, except in the primitive genus _Pliogeomys_ of the middle Pliocene. Occurrence of the plate in _Geomys tobinensis_ is an atavistic trait. Primitive dental patterns occur occasionally in geomyids, as pointed out above, but the frequency of occurrence in _G. tobinensis_ is higher than would be expected.

M1 and M2, like the lower molars, are elliptical in cross-section. Complete enamel plates on the anterior and posterior surfaces are separated by tracts of dentine on the sides of each tooth. M3 is usually suborbicular (sometimes subtriangular) in cross-section. The tooth is not especially elongated posteriorly and usually has no definite heel; therefore, it is not significantly longer than wide. Living species of _Geomys_ rarely have a well defined outer re-entrant fold on M3; less than 10 per cent of the individuals (and usually only one side in each individual in which it occurs) have it, although a shallow inconspicuous groove occurs more frequently. The biprismatic molar characteristic of the ancestral morphotype is less often found in _Geomys_ than in any other living member of the tribe Geomyini. The outer re-entrant fold and biprismatic pattern are more often present in the extinct species _Geomys garbanii_ of the Middle Pleistocene than in other species. Less than 24 per cent of the third upper molars in _Geomys garbanii_ lack a tract of the re-entrant fold and more than 38 per cent have a well developed outer fold (see White and Downs, 1961:13, 18). The bicolumnar pattern, although incomplete, would be clearly evident in those teeth having a well marked re-entrant fold; the pattern occurs less frequently in those teeth with no fold or only a slight one. M3 of geomyids is not usually recovered and, therefore, the occlusal pattern of M3 is unknown in most extinct kinds of _Geomys_. In Recent _Geomys_ the fold is more common in the eastern _pinetis_ species-group than in the western _bursarius_ species-group.

The masseteric ridge on the outer side of the mandible is well developed in all species of the genus. The position of the mental foramen relative to the anterior part of the ridge varies with individuals and according to species. The basitemporal fossa is always present, but is shallower in the late Pliocene and Pleistocene species than in Recent species. The angular process is short.

_Referred species._--The twelve species, five of which are extinct, are as follows:

_quinni_ species-group

*_Geomys quinni_ McGrew, 1944. Geol. Ser., Field Mus. Nat. Hist., 9 (546):49, January 20. Type from Sand Draw local fauna (late Pliocene), Brown County, Nebraska; also known from Broadwater-Lisco local faunas (early Pleistocene), Morrill and Garden counties, Nebraska, Deer Park local fauna (early Pleistocene), Meade County, Kansas.

*_Geomys paenebursarius_ Strain, 1966. Bull. Texas Memorial Mus., 10:36. Type from Hudspeth local fauna (early Pleistocene), Hudspeth County, Texas.

*_Geomys tobinensis_ Hibbard, 1944. Bull. Geol. Soc. Amer., 55:736. Type from Tobin local fauna (middle Pleistocene), Russell County, Kansas; also known from Cudahy local fauna (middle Pleistocene), Meade County, Kansas.

*_Geomys garbanii_ White and Downs, 1961. Contrib. Sci., Los Angeles Co. Mus., 42:1-34, June 30. Type from Vallecito Creek local fauna (middle Pleistocene), San Diego County, California.

*_Geomys bisulcatus_ Marsh, 1871. Amer. Jour. Sci., 3:121. Type from Loup River fossil beds, near Camp Thomas, Nebraska (probably late Pleistocene).

_bursarius_ species-group

*_Geomys parvidens_ Brown, 1908. Mem. Amer. Mus. Nat. Hist., 9:194. (An extinct subspecies of _Geomys bursarius_ according to White and Downs, 1961:6). Type from Conard Fissure local fauna (late Pleistocene), northern Arkansas.

_Geomys bursarius_ (Shaw, 1800). Trans. Linn. Soc. London, 5:227. Type from somewhere in Upper Mississippi Valley, North America.

_Geomys arenarius_ Merriam, 1895. N. Amer. Fauna, 8:139, January 31. Type from El Paso, El Paso County, Texas.

_Geomys personatus_ True, 1889. Proc. U. S. Nat. Mus., 11:159, January 5. Type from Padre Island, Cameron County, Texas.

_pinetis_ species-group

_Geomys pinetis_ Rafinesque, 1806. Amer. Monthly Mag., 2 (1):45, November. Type locality restricted to Screven County, Georgia.

_Geomys colonus_ Bangs, 1898. Proc. Boston Soc. Nat. Hist., 28:178, March. Type from Arnot Plantation, about 4 mi. W St. Marys, Camden County, Georgia.

_Geomys cumberlandius_ Bangs, 1898. Proc. Boston Soc. Nat. Hist., 28:180, March. Type from Stafford Place, Cumberland Island, Camden County, Georgia.

_Geomys fontanelus_ Sherman, 1940. Jour. Mamm., 21:341, August 13. Type from 7 mi. NW Savannah, Chatham County, Georgia.

Genus =Orthogeomys= Merriam

1895. _Orthogeomys_ Merriam, N. Amer. Fauna 8:172, January 31.

1895. _Heterogeomys_ Merriam, N. Amer. Fauna 8:179, January 31 (type, _Geomys hispidus_ Le Conte, 1862).

1895. _Macrogeomys_ Merriam, N. Amer. Fauna 8:185, January 31 (type, _Geomys heterodus_ Peters, 1865).

_Type._--_Geomys scalops_ Thomas, 1894, from Tehuantepec, Oaxaca, México.

_Chronologic range._--Late Pleistocene Wisconsin deposits (San Josecito Cave local fauna, Nuevo León, México) to Recent.

_Description and discussion._--Species of this genus are of medium to large size. The skull is strongly dolichocephalic in most species; the posterior part of the skull is especially narrow. The angular processes are remarkably short, especially in relation to the length of the mandible. The nasals and rostrum are relatively broad and heavy. The pelage is coarse, and often hispid. In some species the hairs are so sparsely distributed that the body appears almost naked, and none has so dense a covering of hair as do other genera. The genus occurs entirely within the tropical life-zones, and most of the external features seem to be associated with adaptation to tropical conditions.

The upper incisor is unisulcate; the sulcus is usually near the inner border of the tooth, but in some species (subgenus _Orthogeomys_) it is more medial, and in a few individuals with an extremely wide groove the outer lip of the sulcus may actually reach the middle of the tooth. The groove is compressed or open. The premolar is a double column united at the mid-point. The two prisms are of approximately equal size, and the lateral re-entrant folds are so compressed that their sides are parallel. Enamel plates cover the anterior surface and border the re-entrant angles in both upper and lower premolars. As in other members of the tribe, the lower premolar has a fourth enamel plate on the posterior surface of the posterior lophid. In the upper premolar, the enamel plate is reduced to a narrow blade on the lingual side of the loph as in the living species of the genus _Zygogeomys_. In the subgenus _Orthogeomys_ the posterior plate is usually absent, and otherwise is narrow and near the lingual border of the tooth.

Each lower molar, in the final stage of wear, consists of a single elliptical column having an enamel plate only on the posterior surface. The first and second upper molars are single elliptical columns having one enamel plate on the anterior surface and another on the posterior surface. The plates are separated by a tract of dentine on each side of the tooth. The third upper molar is partly bilophodont, and the two lophs are separated by a deep outer re-entrant fold. In many of the species an inner re-entrant fold also is retained, but in the adult tooth it is less distinct than the outer. In all of the species the posterior loph is long and forms a conspicuous heel; consequently the crown is significantly longer then wide. Moreover, the posterior loph has an enamel plate on each side. The labial plate always borders the outer re-entrant fold, and in the subgenus _Orthogeomys_ is infrequently separated into two small plates.

The mandible is relatively long. Its masseteric ridge is well developed and massive. The basitemporal fossa is usually deep and well defined; it tends to be shallow in the subgenus _Orthogeomys_, and in young individuals is hardly more than a slight depression.

Key to the Subgenera of _Orthogeomys_

A Frontal wide and greatly inflated; no interorbital constriction; enamel plate on posterior wall of P4 usually absent, although sometimes having small plate, restricted to lingual end of wall. Subgenus _Orthogeomys_ p. 529

A´ Frontal narrow and not greatly inflated; interorbital region decidedly constricted; enamel plate on posterior wall of P4 always present but short and restricted to lingual end of wall.

B Anterior margin of mesopterygoid fossa even with plane of posterior wall of M3; postorbital bar weakly developed; anteroposterior occlusal length of M3 equal to, or less than, combined length of M1 and M2. Subgenus _Heterogeomys_ p. 530

B´ Anterior margin of mesopterygoid fossa decidedly behind plane of posterior wall of M3; postorbital bar strongly developed; anteroposterior occlusal length of M3 more than combined length of M1 and M2. Subgenus _Macrogeomys_ p. 531

Subgenus =Orthogeomys= Merriam

1895. _Orthogeomys_ Merriam, N. Amer. Fauna, 8:172, January 31.

_Type._--_Geomys scalops_ Thomas, 1894, from Tehuantepec, Oaxaca, México.

_Chronologic range._--Known only from the Recent.

_Description._--Skull elongated and narrow (many skulls of nearly uniform breadth throughout), being extreme in dolichocephalic specializations; mandibles long and narrow, rami not spreading laterally, being more nearly parallel-sided than in other subgenera; angular processes short; breadth across zygomata not significantly exceeding breadth across mastoid processes (in many skulls considerably less); interorbital area remarkably broad, lacking deep constriction; frontals between orbits greatly inflated laterally, postorbital prominence inconspicuous; mesopterygoid fossa extending to level of posterior margin of M3; I having sulcus broader than in other subgenera, mostly on inner half of anterior surface but sometimes overlapping mid-line; enamel plate lacking from posterior wall of P4, rarely retaining narrow vestige near lingual border of posterior loph; M3 having distinct heel, bicolumnar pattern with inner re-entrant fold usually minute, occlusal length less than in other subgenera, length less than combined lengths of M1-2; hair generally coarse, sometimes hispid, sparse, in lowland forms, so sparse as to impart appearance of nakedness.

_Referred species and subspecies._--Fourteen taxa:

_Orthogeomys grandis alleni_ Nelson and Goldman, 1930. Jour. Mamm., 11:156, May 9. Type from near Acapulco, 2000 ft., Guerrero.

_Orthogeomys grandis annexus_ Nelson and Goldman, 1933. Proc. Biol. Soc. Washington, 46:195, October 26. Type from Tuxtla Gutierrez, 2600 ft., Chiapas.

_Orthogeomys grandis carbo_ Goodwin, 1956. Amer. Mus. Novit., 1757:5, March 8. Type from Excurano, 2500 ft., Cerro de San Pedro, 20 km. W Mixtequilla, Oaxaca.

_Orthogeomys grandis felipensis_ Nelson and Goldman, 1930. Jour. Mamm., 11:157, May 9. Type from Cerro San Felipe, 10 mi. N Oaxaca, Oaxaca.

_Orthogeomys grandis huixtlae_ Villa, 1944. Anal. Inst. Biol. Univ. Nac. México, 15:319. Type from Finca Lubeca, 12 km. NE Huixtla, 850 m., Chiapas.

_Orthogeomys grandis grandis_ (Thomas, 1893). Ann. Mag. Nat. Hist., ser. 6, 12:270, October. Type from Dueñas, Guatemala.

_Orthogeomys grandis latifrons_ Merriam, 1895. N. Amer. Fauna, 8:178, January 31. Type from Guatemala, exact locality unknown.

_Orthogeomys grandis nelsoni_ Merriam, 1895. N. Amer. Fauna, 8:176, January 31. Type from Mt. Zempoaltepec, 8000 ft., Oaxaca.

_Orthogeomys grandis pluto_ Lawrence, 1933. Proc. New England Zool. Club, 13:66, May 8. Type from Cerro Cantoral, north of Tegucigalpa, Honduras.

_Orthogeomys grandis scalops_ (Thomas, 1894). Ann. Mag. Nat. Hist., ser. 6, 13:437, May. Type from Tehuantepec, Oaxaca.

_Orthogeomys grandis soconuscensis_ Villa, 1949. Anal. Inst. Biol. Univ. Nac. México, 19:267, April 8. Type from Finca Experanza, 710 m., 45 km. (by road) NW Huixtla, Chiapas.

_Orthogeomys grandis guerrerensis_ Nelson and Goldman, 1930. Jour. Mamm., 11:158, May 9. Type from El Limón, in valley of Río de las Balsas approximately 20 mi. NW La Unión, Guerrero.

_Orthogeomys cuniculus_ Elliot, 1905. Proc. Biol. Soc. Washington, 18:234, December 9. Type from Zanatepec, Oaxaca.

_Orthogeomys pygacanthus_ Dickey, 1928. Proc. Biol. Soc. Washington, 41:9, February 1. Type from Cacaguatique, 3500 ft., Dept. San Miguel, El Salvador.

Subgenus =Heterogeomys= Merriam

1895. _Heterogeomys_ Merriam, N. Amer. Fauna, 8:179, January 21.

_Type._--_Geomys hispidus_ Le Conte, 1852, from near Jalapa, Veracruz.

_Chronologic range._--Late Pleistocene, Wisconsin deposits (San Josecito Cave local fauna, Nuevo León) to the Recent.

_Description._--Skull dolichocephalic (less so than in the other subgenera); zygomata more widely spreading than in _Orthogeomys_; ramus and angular process short; interorbital area noticeably constricted; frontals between orbits neither exceptionally broad or inflated; mesopterygoid fossa extending to level of posterior margin of M3; I having sulcus on inner third of anterior surface usually narrower than in subgenus _Orthogeomys_; enamel plate on posterior wall of P4 restricted to lingual half of loph; M3 distinctly biprismatic, posterior loph usually circumscribed by shallow inner re-entrant fold and outer deep fold well developed in all members of genus; posterior loph forming conspicuous heel longer than in subgenus _Orthogeomys_; occlusal length equal to or slightly less than combined lengths of M1-2; hair coarse and hispid but never so sparse as to impart appearance of nakedness.

_Referred species and subspecies._--Eleven taxa:

*_Orthogeomys onerosus_ (Russell, 1960). Univ. Kansas Publ., Mus. Nat. Hist., 9 (21):544, January 14. Type from San Josecito Cave local fauna, Upper Pleistocene, Nuevo León.

_Orthogeomys hispidus cayoensis_ (Burt, 1937). Occ. Papers Mus. Zool., Univ. Michigan, 365:1, December 16. Type from Mountain Pine Ridge, 12 mi. S El Cayo, British Honduras.

_Orthogeomys hispidus chiapensis_ (Nelson and Goldman, 1929). Proc. Bio. Soc. Washington, 42:151, March 30. Type from Tenejapa, 16 mi. NE San Cristobal, Chiapas.

_Orthogeomys hispidus concavas_ (Nelson and Goldman, 1929). Proc. Biol. Soc. Washington, 42:148, March 30. Type from Pinal de Amoles, Querétaro.

_Orthogeomys hispidus hispidus_ (Le Conte, 1852). Proc. Acad. Nat. Sci. Philadelphia, 6:158. Type from near Jalapa, Veracruz.

_Orthogeomys hispidus latirostris_ (Hall and Alvarez, 1961). Anal. Escuela Nac. Ciencias Biol., 10:121, December 20. Type from Hacienda Tamiahua, Cabo Rojo, Veracruz.

_Orthogeomys hispidus negatus_ (Goodwin, 1953). Amer. Mus. Novit., 1620:1, May 4. Type from Gomez Ferias, 1300 ft., about 45 mi. S Ciudad Victoria, 10 km. W Pan American Highway, Tamaulipas.

_Orthogeomys hispidus tehuantepecus_ (Goldman, 1939). Jour. Washington Acad. Sci., 29:174, April 15. Type from mountains 12 mi. NW Santo Domingo and about 60 mi. N Tehuantepec, 1600 ft., Oaxaca.

_Orthogeomys hispidus torridas_ (Merriam, 1895). N. Amer. Fauna, 8:183, January 31. Type from Chichicaxtle, Veracruz.

_Orthogeomys hispidus yucatanensis_ (Nelson and Goldman, 1929). Proc. Biol. Soc. Washington, 42:150, March 30. Type from Campeche, Campeche.

_Orthogeomys lanius_ (Elliot, 1905). Proc. Biol. Soc. Washington, 18:235, December 9. Type from Xuchil, Veracruz.

Subgenus =Macrogeomys= Merriam