Subgenus Spermophilus Cuvier

SPERMOPHILUS CF. S. ELEGANS KENNICOTT, 1863; FIGURE 17.1F,G

REFERRED MATERIAL See appendix 17.1. NISP = 1953, MNI = 400.

SUPRASPECIFIC assignment By far the most abundant sciurid in the Porcupine Cave assemblage represents the morphologically derived ground squirrel subgenus, Spermo-philus (Spermophilus). Evidence supporting this assignment includes a triangular infraorbital foramen, relatively high-crowned cheek teeth, large P3 relative to P4, elongate M3 typically with metaloph, abrupt drop in dorsal surface of the dentary anterior to p4, strong dorsal projection of the coro-noid process, strongly angled angular process (about 90° in posterior view), transversely widened trigonid on p4 (figure 17.2A) with incomplete protolophid (figure 17.1F), high trigonid on p4-m3, and elongate m3 (figure 17.1G). The species is on average significantly larger than S. lateralis (table 17.1).

The Porcupine Cave taxon is allied with the "big-eared" species group (S. beldingi, S. armatus, S. elegans, S. richardsonii; Nadler et al., 1984). It is larger and displays greater development of the metaloph on M3 than "small-eared" species (S. brunneus, S. townsendii complex; Nadler et al., 1984), and is smaller than "long-eared" forms (S. columbianus, S. parryii; Nadler et al., 1984). "Big-eared" species show broad overlap odontometrically (figure 17.2B) and are similar qualitatively, even with complete skulls. Porcupine Cave specimens differ table 17.1

Comparison of S. lateralis and S. cf. S. elegans on Lower and Upper Alveolar Row Measurements

Lower Alveolar Row Upper Alveolar Row

Minimum-Maximum Minimum-Maximum

Taxon

Sample

Mean (SD)

(Sample Size)

Mean (SD)

(Sample Size)

S. lateralis

Total

8.64 (0.44)

8.00-9.52 (24)

8.84 (0.41)

8.39-9.46 (9)

S. cf. S. elegans

Total

9.32 (0.29)

8.47-10.22 (239)

10.23 (0.35)

9.29-11.08 (132)

Velvet Room (A-B)

9.38 (0.30)

8.79-10.22 (46)

10.33 (0.35)

9.60-11.08 (35)

Velvet Room (C-F)

9.25 (0.31)

8.47-9.90 (18)

10.37 (0.48)

9.80-11.05 (9)

Velvet Room (CMNH)

9.39 (0.26)

8.82-9.91 (28)

10.10 (0.27)

9.74-10.46 (10)

Pit

9.16 (0.27)

8.73-9.52 (9)

10.01 (0.19)

9.71-10.29 (7)

Will's Hole

9.24 (0.32)

8.82-10.04 (16)

10.15 (0.42)

9.55-10.95 (10)

Mark's Sink

9.31 (0.30)

8.68-10.20 (66)

10.15 (0.38)

9.29-10.91 (32)

note: S. cf. elegans is given as totals and as selected subsamples.

note: S. cf. elegans is given as totals and as selected subsamples.

FIGURE 1 7.2 (A) Scatterplot of trigonid and talonid width, p4, showing morphometric relationships among ground squirrels and prairie dogs. (B) Scatterplot of trigonid width versus length of p4, showing relationships among various Porcupine Cave samples of S. cf. S. elegans and envelopes of variation of samples of modern "big-eared" ground squirrels.

FIGURE 1 7.2 (A) Scatterplot of trigonid and talonid width, p4, showing morphometric relationships among ground squirrels and prairie dogs. (B) Scatterplot of trigonid width versus length of p4, showing relationships among various Porcupine Cave samples of S. cf. S. elegans and envelopes of variation of samples of modern "big-eared" ground squirrels.

from S. beldingi and S. armatus in typically displaying a prominent trench lingual to the ectolophid and hypoconid of m3 (figure 17.1G) and distinctly raised lateral margins of the skull roof across the interorbital region. Both of these features are shared with S. elegans and S. richardsonii, closely related species of the northern Great Plains (S. richardsonii; Michener and Koeppl, 1985) and appropriate habitats in the central Rocky Mountains and northern Great Basin (S. elegans; Zegers, 1984). S. elegans is present today in the vicinity of Porcupine Cave (Armstrong, 1972).

MORPHOMETRIC VARIATION AND SPECIFIC ASSIGNMENT The derived Porcupine Cave morph did not vary sig nificantly across samples (tests done on samples as indicated in table legends) in measures of alveolar (table 17.1) or p4 length (table 17.2; F = 0.85), suggesting little temporal variation in body size and consistent with a single taxon present across sites. In contrast, two measures of p4 width (trigonid width: F = 7.38,p < 0.00001; talonid width: F = 3.93,p < 0.001) varied significantly across sites (subdivided where possible into stratigraphic samples; table 17.2). For both variables, all significant pairwise differences (Tukey's post-hoc test) distinguished the VR-DMNH (horizon A-B) sample from other samples. Graphic comparison between fossils and extant members of the big-eared species group demonstrated that, on average, fossils exhibit a narrower p4 (figure 17.2B). The table 17.2 Dimensions of p4 for Samples of S. cf. S. elegans

Length p4

Trigonid Width p4

Talonid Width p4

Minimum-

Minimum-

Minimum-

Mean

Maximum

Mean

Maximum

Mean

Maximum

Locality

(SD)

(Sample Size)

(SD)

(Sample Size)

(SD)

(Sample Size)

Velvet Room (A-B)

1.95 (0.08)

1.76-2.07 (22)

2.42 (0.09)

2.23-2.60 (22)

2.31 (0.09)

2.13-2.48 (22)

Velvet Room (C+)

1.99 (0.08)

1.88-2.09 (11)

2.29 (0.13)

2.11-2.46 (11)

2.23 (0.12)

2.05-2.42 (11)

Pit (1)

2.02 (0.09)

1.86-2.17 (28)

2.24 (0.11)

2.07-2.46 (28)

2.16 (0.10)

2.01-2.39 (28)

Pit (2)

1.98 (0.13)

1.74-2.13 (16)

2.23 (0.11)

2.05-2.35 (16)

2.20 (0.15)

1.92-2.45 (16)

Pit (3)

2.00 (0.06)

1.90-2.07 (7)

2.30 (0.09)

2.15-2.40 (7)

2.17 (0.08)

2.03-2.27 (7)

Pit (4)

2.01 (0.07)

1.92-2.09 (8)

2.16 (0.10)

1.99-2.31 (8)

2.12 (0.09)

2.02-2.27 (8)

Pit (5)

1.95 (0.11)

1.72-2.05 (7)

2.18 (0.09)

2.02-2.27 (7)

2.15 (0.11)

1.96-2.33 (7)

Pit (6)

2.01 (0.08)

1.84-2.09 (7)

2.28 (0.18)

2.11-2.52 (7)

2.18 (0.15)

1.99-2.37 (7)

Pit (7-9)

1.96 (0.06)

1.90-2.01 (3)

2.11 (0.07)

2.05-2.19 (3)

2.11 (0.09)

2.05-2.21 (3)

Pit (10-11)

2.02 (0.12)

1.88-2.17 (4)

2.14 (0.07)

2.07-2.23 (4)

2.12 (0.16)

1.94-2.29 (4)

Will's Hole

2.02 (0.12)

1.88-2.25 (10)

2.20 (0.10)

2.07-2.37 (10)

2.16 (0.10)

2.03-2.42 (10)

Mark's Sink

1.98 (0.12)

1.72-2.21 (17)

2.27 (0.13)

2.05-2.46 (17)

2.22 (0.12)

1.96-2.37 (17)

Badger Room

2.10 (0.04)

2.07-2.13 (2)

2.27 (0.08)

2.21-2.33 (2)

2.31 (0.11)

2.23-2.39 (3)

Generator Dome

2.13 (-)

2.29 (—)

2.25 (—)

note: Interlocality statistical comparisons pooled Pit levels 7-11 and excluded samples from the Badger Room and Generator Dome because of small sample size.

note: Interlocality statistical comparisons pooled Pit levels 7-11 and excluded samples from the Badger Room and Generator Dome because of small sample size.

sample from VR-DMNH falls almost entirely within the envelope of variation of modern S. elegans but is smaller than average for S. richardsonii; other Porcupine Cave samples clustered below these taxa (figure 17.2B).

Stratigraphic variation in the Pit and VR-DMNH sequences further complicates systematic interpretation (figure 17.3A). The sample from Pit level 6 exhibits two size clusters. Larger specimens seem anomalous compared to adjacent strati-graphic samples, breaking what otherwise might be viewed as a progressive if irregular trend toward increasing p4 width through time (assuming that VR-DMNH is younger than the Pit, a point that is discussed later in this chapter).

Given available evidence, three species level interpretations deserve consideration:

1. Fossils may represent a single, evolving lineage continuous with extant S. elegans and should thus be assigned to that species, an interpretation suggesting a long history for S. elegans distinct from S. richardsonii. In contrast, Neuner (1975) inferred post-Pleistocene divergence of S. richardsonii and S. elegans based in part on morphological intermediacy of the widespread fossil representative of the lineage, known primarily from the Great Plains (Neuner, 1975).

2. Fossils may represent a single lineage, as described previously, but the lineage should be subdivided into two chronospecies: one for older samples, with samples from upper VR-DMNH assigned to S. elegans. This interpretation again conflicts with that of Neuner (1975) and is complicated by the presence of S. elegans-type specimens from level 6 in the Pit.

3. The fossil sample includes two distinct but related lineages: an older lineage dominant in the Pit (and other old sites), and S. elegans, which shows up at least by level 6 but which is never dominant until the time represented by the upper horizons of VR-DMNH. This interpretation is intriguing, but it is complicated by the absence of other clear evidence for two morphological clusters at any given time horizon.

At present, the taxonomic status of the fossil samples remains unresolved. Pending further study, involving additional characters and comparisons with other Pleistocene samples of the S. richardsonii-S. elegans group, I assign these fossils to S. cf. S. elegans.*

In addition to the material already described, notes of A. D. Barnosky written in 1991 document the presence of 29 isolated Spermophilus teeth from level 8 in the Pit, at least 24 of which (MNI = 3) may have been referable to S. cf. S. elegans according to Barnosky, as inferred from the descriptions and sketches that were recorded. Unfortunately, these specimens

* Editor's Note: Since this chapter was written, the author has published a quantitative analysis that supports the identification of the Porcupine Cave specimens as an "early, temporally variable segment in the lineage [of S. elegans]" (Goodwin, 2002:185).

Filtro Oleo Colhedora Tratores

FIGURE 17.3 Stratigraphic and interlocality patterns in (A) trigonid width of p4 of S. cf. S. elegans (showing mean, standard deviation, and range; displaying individual specimens in some cases) and (B) relative frequency of selected sciurid taxa (as proportion of MNI). Locality abbreviations are given in the Materials and Methods section.

FIGURE 17.3 Stratigraphic and interlocality patterns in (A) trigonid width of p4 of S. cf. S. elegans (showing mean, standard deviation, and range; displaying individual specimens in some cases) and (B) relative frequency of selected sciurid taxa (as proportion of MNI). Locality abbreviations are given in the Materials and Methods section.

were subsequently lost and so were unavailable for examination in preparing this chapter. Noting their presence, however, is important in that the specimens document the presence of Spermophilus in level 8 as well as in the sub- and superjacent levels.

DISCUSSION A ground squirrel related to the S. richard-sonii-S. elegans species group was widely distributed across the Great Plains in the Pleistocene (Neuner, 1975), apparently present from the middle Irvingtonian (Cudahy local fauna; Paulson, 1961) to the end of the Pleistocene. The Porcupine Cave record indicates that this lineage was also present (and apparently extremely abundant) in appropriate habitats of the central Rocky Mountains well back in the Pleistocene. Ongoing study may clarify the relationships between the Great Plains and Porcupine Cave populations of this lineage.

Goodwin (1998) reported a dental abnormality present in modern members of the S. richardsonii-S. elegans lineage, concentrated in an interspecific hybrid zone in Montana, and known from a fossil in Nebraska. The abnormality involves bilateral expression of a supernumerary distal upper molar and always results in abnormal development of the two distal upper teeth ("M3A" and "M3B"). This abnormality was not observed in a large sample of M3s from Porcupine Cave assigned to S. cf. S. elegans (n > 500).

Porcupine Cave is near the southeastern limit of the current range for S. elegans (Armstrong, 1972). In Colorado, the species occupies grassland and semiarid shrubland and has a diet consisting principally of grasses and forbs (Armstrong, 1972; Fitzgerald et al., 1994). S. elegans is reported to displace S. lateralis when they co-occur (Fitzgerald et al., 1994), a relationship that may partially explain the greater representation of the former in almost all samples taken from the cave.

SPERMOPHILUS (SPERMOPHILUS) SP.

REFERRED MATERIAL Badger Room: L p4 (DMNH 34201). Mark's Sink: R dentary with p4-m2 (DMNH 37054). NISP = 2, MNI = 2.

identification and discussion This sciurid is distinguished from S. cf. S. elegans by its larger size; substantially greater buccal expansion of the hypoconid on p4, resulting in a relatively greater ratio of talonid width to trigonid width (figure 17.2A); bulging mesial margin of p4; and more robust dentary. However, it is linked with advanced ground squirrels, S. (Spermophilus), by the widened trigonid on p4 and the strongly angled angular process (circa 90° in posterior view). Both sites with this sciurid appear to be old on the basis of other evidence (summarized later in this chapter), but specimens differ from all described Blancan or Irvingtonian sciurids.

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