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Journal of Paleontology 91(6):1244–1257
protolophid on p4 (Fig. 4.6, compare with Fig. 3.1). They differ from coeval Urocitellus cf.U. richardsonii (Sabine, 1822) in much less relative trigonid width on p4 (Fig. 5.3), and relatively less-elongate M3 (Fig. 7.3) and m3 (Fig. 8.1) that lack the defined metaloph and talonid basin trench, respectively, of Urocitellus (Figs. 7.4, 8.2). Middle Pleistocenem3s from Cudahy plot with the holotype
of P. lorisrusselli and are smaller than extant P. franklinii (Fig. 6.2), but some later p4s were larger (Fig. 5.1). In addition, Eshelman and Hibbard (1981) tentatively identified P. franklinii in the early Pleistocene Nash 72 assemblage, explicitly noting that the teethwere larger than in P. lorisrusselli.Weprovisionally accept their interpretation based on published measurements, but do so with question because we were not able to inspect the specimens. We conclude that the Meade Basin supported a single, size-
variable lineage of Poliocitellus from the Middle (and perhaps early) to Late Pleistocene, with P. lorisrusselli representing an episode of reduced size.We assign all specimens to P. franklinii, which has priority.
Genus Urocitellus Obolenskij, 1927 Urocitellus? cragini (Hibbard, 1941a) Figure 4.8
1941a Citellus cragini Hibbard, p. 204, pl. 1, fig. 13. 1980
1994 Spermophilus cragini Kurtén and Anderson, p. 214.
Spermophilus? cragini Goodwin and Hayes, p. 283, fig. 3.
Holotype.—KUVP 6168, right maxilla with M1–M3 from Borchers, Meade Co., KS (Hibbard, 1941a, pl. 1, fig. 13).
Remarks.—Urocitellus? cragini (Hibbard, 1941a) represents a large ground squirrel initially described solely on the holotype (Hibbard, 1941a) and subsequently described more fully and formally assigned to the derived subgenus Spermophilus (genus Urocitellus after Helgen et al., 2009) based on a larger sample (Goodwin and Hayes, 1994). It has only been reported from the type locality. The questioned assignment to Urocitellus? follows Goodwin and Hayes (1994), because U.? cragini could represent a small, dentally underived prairie dog (see below). It represents the first occurrence of a ground squirrel with proportionally wide p4 in the Meade Basin record (Fig. 5.3), a morphology shared by Urocitellus and Cynomys (Goodwin, 2009).
Urocitellus? cragini differs from all extant species of
Urocitellus in the presence of a complete protolophid on most p4s (Fig. 4.8), a feature characteristic of Cynomys; but it differs from all Cynomys in the absence of a well-developed lophulid on the talonid of m1–m2, presence of an incomplete metalophid on m3, more circular P3, and less-elongate M3 and m3, all features of Urocitellus (Goodwin and Hayes, 1994). Urocitellus? cragini was a large squirrel (Table 2, Fig. 4.8) that was much larger than middle Pleistocene and later species assigned to the genus (Table 2, Figs. 5.1, 5.2, 6.1). Its dentition resembles that of the extant Arctic ground squirrel, Urocitellus parryii (Richardson, 1825) in p4 and P4 length, but exhibits much wider teeth (Goodwin and Hayes, 1994, fig. 1).
Urocitellus cf. U. richardsonii (Sabine, 1822) Figures 7.4, 8.2
1822 Arctomys richardsonii Sabine, p. 589 [For listing of synonyms in the literature of modern Urocitellus richardsonii, see Michener and Koeppl, 1985, p. 1]. 1967 Citellus kimballensis Kent, p. 18, figs. 1–3.
Holotype.—Holotype not designated. Type locality Carlton House, Saskatchewan, Canada.
Remarks.—Fossils assigned to Urocitellus cf. U. richardsonii are smaller than fossils of U.? cragini and exhibit much greater trigonid width of p4 than in Otospermophilus, Ictidomys, and Poliocitellus (Fig. 6.1). The M3 usually displays a prominent metaloph (Fig 7.4), and m3 characteristically exhibits a distinct talonid basin trench adjacent to the ectolophid (Fig 8.2), in both cases resembling Cynomys (Figs. 7.5, 8.3.1). Morphometrically, many fossil m3s fall within the envelope of variation defined by the extant sister species U. richardsonii and Urocitellus elegans (Kennicott, 1863), although Cudahy teeth are distinctly smaller than teeth from earlier and later assemblages (Fig. 6.2). There is considerable dental morphological overlap between
extant U. richardsonii and U. elegans (Goodwin, 2002). Urocitellus elegans inhabits open habitats in the central Rocky Mountains and northern Basin and Range (Zegers, 1984), and was present at high elevations in central Colorado (Porcupine Cave) during the Middle Pleistocene (Goodwin, 2002). In contrast, U. richardsonii is an occupant of the northern Great Plains with closest extant populations ~775km to the NNE in SE South Dakota (Michener and Koeppl, 1985). We tentatively refer the Meade Basin fossil Urocitellus to Urocitellus cf. U. richardsonii on geographic grounds because a number of other northern Great Plains rodent species dispersed southward into the Meade Basin,
Figure 8. Lower right m3 fossils of (1) P. franklinii (UMMP 117771) and (2) Urocitellus cf. U. richardsonii (UMMP 117732), both from Cudahy, and (3.1, 3.2)of C. hibbardi from Nash (FHSM VP-18209). (3.2) represents an oblique, occlusodistal view of the trigonid. Attributes noted in text are labelled; lam = lingual arm of metapholophid; ctp = closure of trigonid pit. Scale bar = 1mm.
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