1254 Cynomys sp.


Remarks.—Two well-preserved fossils (lower jaws with most teeth) from Robin’s Roost, Beaver Co., OK (approximately time-equivalent with Cudahy) document the presence of a large prairie dog in the Meade Basin south of the Cimarron River. The m3s are similar to those of C. niobrarius based on presence of a bridge between the ectolophid and talonid on m3, but the p4s also display a relatively narrower trigonid than expected for white-tailed prairie dogs. The specimens are currently under study and are referred here to Cynomys sp. Asingle large, somewhat worn M1 or M2 from the Cudahy


time-equivalent Sunbrite assemblage (KUVP 6703) clearly represents a large Cynomys, but lacks diagnostic features to allow species assignment. An upper molar was likewise attributed to Cynomys from the Robert local fauna (Schultz, 1969). We were unable to examine this specimen, but generic identification is probably correct given that Cynomys molars are much larger than those of any other ground squirrel known from the Late Pleistocene of the Meade Basin, and thus unlikely to be misidentified. We identify both specimens as Cynomys sp.


Cynomys? new sp. Figure 4.9


Remarks.—Asingle p4 from Sunbrite (KUVP 6704) documents a second prairie dog or prairie dog-like Urocitellus (Fig. 4.9) from that assemblage. This p4 displays great relative width (identified in Fig. 5.3) and a well-developed protolophid that lacks a distinct notch at its attachment with the protoconid (Fig. 4.9), in both respects resembling Cynomys more than Urocitellus. However, it is much smaller than all other known Cynomys (Table 2), plotting between Urocitellus cf. U. richardsonii and U.? cragini in length of p4 (identified in Fig. 5.1). KUVP 6704 represents an undescribed species, but more complete material will be needed to support a description. Generic assignment was queried because it could represent either a small Cynomys or highly derived Urocitellus.


Genus Paenemarmota Hibbard and Schultz, 1948 Paenemarmota barbouri Hibbard and Schultz, 1948


1948 Paenemarmota barbouri Hibbard and Schultz, p. 19, pls. 1–3.


Holotype.—KUVP 6994, left lower jaw with I, p4-m3. KUVP Locality 22, Rexroad Formation, sec. 34, T.34S., R.30W (Hibbard and Schultz, 1948).


Remarks.—Paenemarmota includes giant ground squirrels from the late Miocene and Pliocene (Fig. 6.1; Goodwin, 2008). Paenemarmota barbouri Hibbard and Schultz, 1948 had an estimated body mass of ~16 kg, extrapolated from length of p4 (Goodwin and Bullock, 2012), and was present at Fox Canyon within the Meade Basin sequence (Table 1).


Paenemarmota sawrockensis (Hibbard, 1964)


1964 Marmota sawrockensis Hibbard, p. 118, fig. 1. 1988 Paenemarmota sawrockensis Voorhies, p. 168, figs.3,4.


Journal of Paleontology 91(6):1244–1257


Remarks.—Paenemarmota sawrockensis (Hibbard, 1964) differed from P. barbouri in smaller size (Table 2, estimated body mass ~10 kg; Goodwin and Bullock, 2012), less molariform p4, and more elevated point of attachment of the metalophid on the metaconid (Voorhies, 1988). It was present at Sawrock Canyon within the Meade Basin. Recognition of P. sawrockensis and P. barbouri as


different lineages rather than temporal variants of a single lineage is supported by the relationship between P. barbouri and Paenemarmota mexicana (Wilson, 1949). The latter species was present in late Miocene and early Pliocene localities of northern Mexico (summarized in Goodwin, 2008), and shared with P. barbouri a molariform p4 and minimally developed metalophid on lower molars. These species were either closely related or conspecific (Repenning, 1962). If this relationship is correct, the P. barbouri–P. mexicana lineage must be distinct from P. sawrockensis because populations of the former lineage were present in the fossil record both prior and subsequent to deposition of the Saw Rock Canyon assemblage with P. sawrockensis.


Discussion


Temporal patterns and environmental reconstruction.—The Meade Basin sciurid record is more diverse than previously understood, with at least seven genera and 14 species present in the composite early Pliocene to Late Pleistocene sequence (Table 1). The record is discontinuous (Fig. 2), with fossil assemblages clustering at a few discrete time intervals (Fig. 5), but broad faunal patterns can be inferred. Extinct giant ground squirrels (Paenemarmota) were


restricted to the early Pliocene in the Meade Basin, although P. barbouri remained on the southern High Plains into the late Pliocene (Dalquest, 1975). In contrast, I. meadensis and O. rexroadensis persisted through the Pliocene, with the former ranging into the earliest Pleistocene at Borchers (Fig. 5). A second, larger species of Otospermophilus was likely also present in the early Pliocene (Fig. 5). Antelope ground squirrel fossils (Ammospermophilus) were relatively uncommon, present at two early Pliocene localities, and possibly present in the late Pliocene (Fig. 5.2, Table 1). The early Pleistocene Borchers assemblage displays a


diverse sciurid assemblage with transitional character. Ictidomys meadensis persisted from the Pliocene. The larger-bodied Otospermophilus was notably absent, but a similar-sized, dentally derived species probably representing the Holarctic genus Urocitellus (U.? cragini) was abundant. Two additional species of Urocitellus were likely present, including the lineage leading to the extant U. richardsonii (Table 1). Prairie dogs (Cynomys) were absent. The transition between Borchers and slightly younger early


Pleistocene faunas in the Meade Basin (e.g., Short Haul, Aries, Rick Forester, and Nash 72) was abrupt, both taxonomically (Table 1) and temporally (Fig. 5). None of the ground squirrels present at Borchers was recorded at higher localities in the same outcrops, although Urocitellus cf. U. richardsonii returned later in the Pleistocene. Ictidomys tridecemlineatus first appeared in the Meade Basin along with an extinct prairie dog, C. hibbardi. Cynomys hibbardi was present by the late Pliocene in northern


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