Subfamily Sciurinae


REFERRED MATERIAL Pit level 1-R M1-2 (CM 66103); level 2-L M1-2 (UCMP 175231); L M3 (CM 66506); 2 R m1-2 (UCMP 180964-180965); level 3-L M1-2 (UCMP 180968); L, R m1-2 (UCMP 180966-180967); level 4-L, R P4 (UCMP 180973-180974); R M1-2 (UCMP 180975); L, R m1-2 (UCMP 180969-180970); L, R m3 (UCMP 180971-180972); level 5-L, R M1-2 (UCMP 180977-180978); L m1-2 (UCMP 180976); level 6-R M1-2 (UCMP 180980); R m1-2 (UCMP 180979); level 7-L m1-2 (UCMP 180981); L, R m3 (UCMP 180982-180983). NISP = 23, MNI = 7.

IDENTIFICATION AND DISCUSSION Fossils referred to Tamiasciurus clearly represent a small tree squirrel. Upper cheek teeth bear a broad, mesiodistally expanded protocone; low metaloph and protoloph; and prominent mesostyle (figure 17.1A). Lower cheek teeth are likewise low crowned, bear a conspicuous entoconid notch, exhibit a prominently swollen ectolophid, and usually have a distinct mesostylid (on m1-m2; figure 17.1B). This combination of features is shared by Tamiasciurus and Sciurus, is never found in ground squirrels, and is not typical of Glaucomys (flying squirrels). Teeth of the latter commonly lack mesostyles and mesostylids, and furthermore they bear a distinct groove on the mesial face of the protoconid of lower cheek teeth at the junction of proto-lophid and protoconid. A preliminary faunal list reported cf. Glaucomys from Porcupine Cave (Anderson, 1996), but I did not observe the Glaucomys morphotype in this survey.

The Porcupine Cave specimens are referred to Tamiasciurus, not Sciurus, on the basis of small size and morphology of the trigonid on m1-m3. In Tamiasciurus and fossil specimens, the trigonid pit is characteristically bounded mesially by a pro-tolophid at least as high as or higher than the distally bounding metalophid. In contrast, Sciurus characteristically exhibits a very low protolophid adjacent to this pit. The trigonid pit on Sciurus thus often opens mesially, especially with wear. Both Sciurus (Barnosky and Rasmussen, 1988) and Tamiasciurus (Barnosky and Rasmussen, 1988; Anderson, 1996) were previously listed from the cave, but I found no evidence of the former in my study.

FIGURE 1 7.1 Fossil teeth of Tamiasciurus, Spermophilus, and Cynomys. (A) R M1-2 (UCMP 180980) and (B) L m1-2 (UCMP 180966) of Tamiasciurus hudsonicus (both from the Pit). (C) R P4 and M2 of Spermophilus, possibly near S. meadensis (DMNH 28335, Generator Dome). (D) R P4 of Spermophilus (?Otospermophilus) sp. (UCMP 180950, Pit level 10). (E) R p4 of S. lateralis (DMNH 37288, Will's Hole) and (F) L p4 of S. cf. S. elegans (UCMP 180193, Pit level 8A). (G) L m3 of S. cf. S. elegans (UCMP 180493, Pit level 3) and (H) R m3 (reversed) of Cynomys cf. C. leucurus (180155, Pit level 3). Scale bar beneath G applies to all but H, with its own scale bar. Morphological terms are labeled on D and F.

T. hudsonicus is one of two extant species in the genus and the only one found in Colorado (Armstrong, 1972), or, for that matter, east of the Pacific states (Hall, 1981). Referral of fossil specimens to this lineage is thus very probable on bio-geographic grounds. This species has previously been documented in the Irvingtonian (Conard Fissure, Cumberland Cave, Trout Cave; Kurten and Anderson, 1980) as well as in numerous Rancholabrean sites (Kurten and Anderson, 1980).

Of all Porcupine Cave sciurids, T. hudsonicus is the strongest indicator of forest habitat within the sampling range of the cave. The species is characteristic of subalpine and montane forests in Colorado (Armstrong, 1972; Fitzgerald et al., 1994) but avoids ponderosa pine forests with Sciurus aberti, a species not observed in the Porcupine Cave assemblage. T. hudsonicus may also utilize riparian stands of cottonwood, although it is less abundant in such habitat (Armstrong, 1972; Fitzgerald etal., 1994).


REFERRED MATERIAL Velvet Room (DMNH): R maxillae with P4-M1 (DMNH 29100); M1-M3 (DMNH 38866); R den-tary with m1-m3 (DMNH 10487); L dentary with p4-m1 (DMNH 12014). Velvet Room (CM)-L maxilla with P4-M3 (CM 49237). Pit level 1-R dentary with p4-m1 (CM 65327); R

m1-2 (UCMP 180952); level 2-2 R M1-2 (UCMP 180954180955); L M1-2 (CM 66524); R edentulous dentary (CM 65502); R m1-2 (UCMP 180953); level 3-L M3 (UCMP 180957); R m1-2 (UCMP 180956); level 4-L P4 (UCMP 180960); R M1-2 (UCMP 180961); R M3 (UCMP 180962); L p4 (UCMP 180958); L m1-2 (UCMP 180959); level 5-R M1-2 (UCMP 180963). NISP = 20, MNI = 11.

IDENTIFICATION AND DISCUSSION Chipmunks (Tamias) can be distinguished from all other North American sciurids based on a combination of small size, the presence of a notch mesiobuccal to the protoconid on m1-m3, and other dental details. Three species occur today in or near the vicinity of Porcupine Cave. The least chipmunk (Tamias minimus) and Colorado chipmunk (T. quadrivittatus) are mapped as locally present, and the Uinta chipmunk (T. umbrinus) occurs less than 50 km to the west (Armstrong, 1972).

Definitive identification of chipmunk species based on dental remains is difficult, but T. minimus is typically smaller than other species (e.g., Goodwin and Reynolds, 1989). Measurement of the alveolar row on three Porcupine Cave dentaries (mean = 5.07 mm, SD = 0.07, minimum-maximum = 5.005.14 mm) indicates a very small chipmunk. Armstrong (1972) reported lower tooth row (not alveolar) measurements for modern chipmunks in Colorado (ranges: T. minimus, 4.4-

5.5 mm; T. quadrivittatus, 5.5-6.3 mm; T. umbrinus, 5.55.9 mm). These values are probably less than equivalent measurements of the alveolar row, yet fossils still fall within the range of T. minimus but outside the range of other species. On this basis, I refer the fossil specimens to T. minimus.

T. minimus has been reported from a number of late Quaternary sites (e.g., Harris, 1985; Goodwin and Reynolds, 1989) but, to my knowledge, has not previously been reported from the Irvingtonian. This species is the most widespread extant species of North American chipmunk, ranging across much of Canada and southward across large regions of the western United States (Hall, 1981). In Colorado today, T. minimus is common, widespread geographically, and eurytopic: it occurs from greasewood flats to habitats above treeline (Armstrong, 1972). The paleoecological significance of its occurrence is thus difficult to assess.


REFERRED MATERIAL Fossil material was not surveyed systematically for this chapter. However, detailed phylogeo-graphic studies on Marmota from the Pit were performed by Polly (2003), and the response of Marmota populations to climate change was examined in his paper and in chapters 24 and 25; the material referred to Marmota is listed in appendix 25.1.

IDENTIFICATION AND DISCUSSION Cursory examination indicates the presence of marmot specimens at several sites in Porcupine Cave (listed from the Pit, Gypsum Room, VR-CM, and BR [Barnosky and Rasmussen, 1988]; observed in the VR-DMNH and MS assemblages). The species there today is Marmota flaviventris, which occupies a broad geographic range and a variety of habitats in the montane West (Hall, 1981), ranging from semidesert to alpine meadows (Frase and Hoffmann, 1980). Although the species does not require mesic conditions, it is evidently sensitive to a lack of winter-spring precipitation because of its dependence on green fodder in spring and early summer (Harris, 1970). The species is common and abundant in late Pleistocene sites of the montane West (e.g., Harris, 1985). Previous work has documented sharp changes in relative abundance of marmot in the Pit sequence (Barnosky et al., 1996).

There is doubt that M. flaviventris is the species represented in the Pit sequence. Polly's work (2003) placed the Pit specimens in the M. monax clade based on a morphometric study of the m3. However, it still is not clear whether the Porcupine Cave specimens represent M. monax or a species that is too distantly related to be placed in the M. monax crown group. Until this situation is resolved the marmots here are simply assigned to Marmota sp.

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