Cynomys sp.—Prairie Dogs // Cynomys gunnisoni—Gunnison's Prairie Dog // Cynomys ludovicianus—Black-tailed Prairie Dog // Cynomys mexicanus—Mexican Prairie Dog
Prairie dogs are relatively large, social ground squirrels that associate in "towns". Historically they have been distributed widely from within the Great Plains and westward. Two subgenera usually are recognized: C. (Cynomys), the black-tailed prairie dogs, and C. (Leucocrossuromys), the white-tailed group.
Fig. 1. Black-tailed Prairie Dog (Cynomys ludovicianus), El Paso Zoo. Photograph by A. H. Harris.
Two species occur in our region today, though they have been extirpated from much of the historic range by poisoning. Roughly, the northwestern half of Texas and the southeastern 2/3 of New Mexico were within the range of Cynomys ludovicianus, the Black-tailed Prairie Dog. In New Mexico, it has been basically exterminated from about Santa Fe Co. south and southwest. The other species, Cynomys gunnisoni (Gunnison's Prairie Dog), still inhabits much of the northwestern third of New Mexico from Colfax Co. southeast to northern Sierra Co. In Arizona, it inhabits roughly the northeastern third of the state. It apparently has not occurred sympatrically with C. ludovicianus.
The Black-tailed Prairie Dog is primarily a short-grass prairie animal and, like a number of other animals associated with grassland, extended westward in the far southern part of New Mexico and into adjacent southeastern Arizona. It appears that it was less common in Lower Sonoran Desert habitats than at somewhat higher elevations.
Gunnison's Prairie Dog is elevationally pliant, occurring from low elevations into meadows in high montane areas, having been reported as high as 12,000 ft in Colorado (Findley et al. 1975). It occur north to south-central Colorado, but is replaced to the northwest and north by other species of the subgenus.
Dalquest (1988), in a study of fossil prairie dogs of Texas, pointed out differences in lower molars, especially m3, between the subgenera of prairie dogs. Fig. 2 shows the major differences between the m3s of the two subgenera. However, Semken (1966) found in samples of prairie dog third lower molars that 90% of the C. gunnisoni molars showed the C. ludovicianus condition and 91% of the latter showed the C. gunnisoni type. Likewise, Czaplewski and Smith (2012) found significant variability.
Fig. 2. Lower third molars of Cynomys gunnisoni (left; left m3, Isleta Cave No. 2, UTEP 46.274) and Cynomys ludovicianus (right; right m3 reversed for comparison; Khulo site, UTEP 21.20). el, ectolophid; ml, mesolophid; ms, mesostylid; tb, trigonid basin; tp, talonid platform; tv, talonid valley.
In Fig. 2, the m3 of C. gunnisoni is in Dalquest's wear stage 2, whereas that of C. ludovicianus is in wear stage 1. However the two are easily compared. In C. gunnisoni, there usually is a stylid internal to the ectolophid and the talonid platform that, with wear, joins a ridge (mesolophid) that runs along the anterior of the talonid platform, dividing the talonid valley into anterior and posterior parts. This mesolophid also restricts the talonid platform to a more or less triangular shape (according to Dalquest, even when the dividing stylid is absent). In C. ludovicianus, the talonid valley is continuous, at least until a late wear stage; the talonid valley is described by Dalquest as a flattened "W" shape.
Literature. Czaplewski and Smith 2012; Dalquest 1988; Findley et al. 1975; Semken 1966.
The massiveness and other characters of the postcranial skeleton often allow assignment to the genus, but not to the species. The same is true of some cranial and mandible fragments.
Morgan and Lucas (2003:283) report a Cynomys mandible from southwest of Santa Fe of apparent late Blancan age that "most closely resembles the extinct species C. hibbardi...". It is mapped here as Cynomys sp., and no site account has been made.
Late Blancan: About 2 km west of Turquoise Hill (Morgan and Lucas 2003).
Early/Early-Mid Wisconsin: Rm Vanishing Floor (Harris 1993c).
Mid Wisconsin: U-Bar Cave (Harris 1987).
Mid/Late Wisconsin/Holocene: Jimenez Cave (Messing 1986).
Late Wisconsin:Dust Cave (Harris and Hearst 2012); Pendejo Cave (Harris 2003); U-Bar Cave 13-14 ka (Harris 1989); U-Bar Cave 14-15 ka (Harris 1989); U-Bar Cave 15-18 ka (Harris 1989); U-Bar Cave 18-20 ka (Harris 1989).
Literature. Harris 1987, 1989, 1993c, 2003; Harris and Hearst 2012; Messing 1986; Morgan and Lucas 2003.
Tebedge (1988) identified Cynomys leucurus from Dark Canyon Cave. This apparently was a matter of confusion between C. leucurus (White-tailed Prairie Dog), that has a more northern distribution, and C. gunnisoni, which occurs now in the northwestern third of New Mexico. Both are of the subgenus Leucocrossuromys, in contrast to the members of the subgenus Cynomys, which includes the Black-tailed Prairie Dog that currently occupies southeastern New Mexico.
Fig. 1. Ventral view of the skull of Cynomys gunnisoni. The convergence posteriorly of the upper toothrows is typical of all prairie dogs and will separate them from other sciurids of similar size.
Quaternary: Hatch Cemetery (Harris 1993c: ?).
Mid Wisconsin: Pendejo Cave (Harris 2003); Screaming Neotoma Cave (Glennon 1994); U-Bar Cave (Goodwin 1995).
Mid/Late Wisconsin: Dark Canyon Cave (Tebedge 1988: C. leucurus).
Mid/Late Wisconsin/Holocene: Sierra Diablo Cave (UTEP).
Late Wisconsin: Alpine (UTEP: cf.); Animal Fair 18-20 ka (Harris 1993c); Harris' Pocket (UTEP, earlier as subgenus Leucocrossuromys); Screaming Neotoma Cave (Glennon 1994); Lower Sloth Cave (Logan 1983: cf.); Steeruwitz Hills #1(4) (Van Devender and Bradley 1990: cf.); U-Bar Cave (Goodwin 1995).
Late Wisconsin/Holocene: Howell's Ridge Cave (Harris 1993c); Isleta Cave No. 1 (Harris 1993c); Isleta Cave No. 2 (Harris 1993c); Williams Cave (Ayer 1936: cf.).
Literature. Ayer 1936; Dalquest 1988; Glennon 1994; Goodwin 1995; Harris 1993c, 2003; Logan 1983; Tebedge 1988; Van Devender and Bradley 1990.
Cynomys ludovicianus is more massively built than C. gunnisoni. In elements of comparable age, this alone often can identify an element as one or the other. Such elements as the dentary (Fig. 1) are separable from other sciurids by the combination of size and robustness.
Fig. 1. Left dentary of Cynomys ludovicianus.
Medial Irvingtonian: SAM Cave (Rogers et al. 2000).
Rancholabrean: La Playa (White et al. 2010); Tramperos Creek (Morgan and Lucas 2005).
Mid/Late Wisconsin: Dark Canyon Cave (Tebedge 1988); Pit N & W Animal Fair (Harris 1993c).
Mid/Late Wisconsin/Holocene: Sierra Diablo Cave (UTEP).
Late Wisconsin: Blackwater Loc. No. 1 (Slaughter 1975); Folsom (Morgan and Lucas 2005); Navar Ranch (Van Devender et al. 1987); Ventana Cave (Colbert 1950).
Late Wisconsin/Holocene: Burnet Cave (Schultz and Howard 1935); Conkling Cavern (Harris 1993c: cf.); Fowlkes Cave (Dalquest and Stangl 1984b); Howell's Ridge Cave (Harris 1993c); Pendejo Cave (Harris 2003); SAM Cave (Rogers et al. 2000).
Literature. Colbert 1950; Dalquest and Stangl 1984b; Harris 1993c, 2003; Morgan and Lucas 2005; Rogers et al. 2000; Schultz and Howard 1935; Slaughter 1975; Tebedge 1988; Van Devender et al. 1987; White et al. 2010.
Cynomys mexicanus is a member of the subgenus Cynomys, the black-tailed prairie dog group. Currently it is limited to a small area in northeastern Mexico. Goodwin (1985) studied fossils from the Lost Valley site in Dry Cave and tentatively assigned them to this species on the basis of overall similarity in size and in an elongated diastema; he did note, however, that the fossils seem to be generally more robust and with deeper lower jaws, though within the range of variation of modern specimens. Goodwin also noted that genetic information from modern populations of C. mexicanus suggests separation from Cynomys ludovicianus about 42,000 years ago (McCullough and Chesser 1987). Goodwin hypothesized that the Lost Valley taxon, then, may represent the early history of the species, relatively shortly after speciation.
Early/Early-Mid Wisconsin: Lost Valley (Goodwin 1995: cf.).
Literature. Goodwin 1995; McCullough and Chesser 1987.
Last Update: 20 Nov 2013