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Principal component analysis of cranial morphology among U. mollis sensu lato subspecies based on a) 14 traditional linear measurements and b) 24 two-dimensional geometric morphometric (GMM) landmarks. The GMM data are representative of the ventral cranium only.

Principal component analysis of cranial morphology among U. mollis sensu lato subspecies based on a) 14 traditional linear measurements and b) 24 two-dimensional geometric morphometric (GMM) landmarks. The GMM data are representative of the ventral cranium only.

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The “small-eared” species group of Urocitellus ground squirrels (Sciuridae: Xerinae: Marmotini) is endemic to the Great Basin, United States, and surrounding cold desert ecosystems. Most specific and subspecific lineages in this group occupy narrow geographic ranges, and some are of significant conservation concern; despite this, current taxonomy r...

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Context 1
... GMM and traditional linear measurements. The latter were more useful in discriminating subspecies, so we limit discussion to these. In a PCA based on 14 log10-transformed measurements from 40 adult specimens (including 9 U. m. artemesiae, 8 U. m. idahoensis, and 23 U. m. mollis), the first 4 components accounted for 75.7% of the total variance (Fig. 4). All variables had positive loadings on the first component, and most (12 of 14) were of moderate to high magnitude (0.533 to 0.915) indicating that the first component reflected size variation. Component 2 accounted for an addition 12.1% of the total variance, with the highest magnitude negative loadings for the length of the bulla ...
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... of the ventral cranium did not strongly discriminate northern and southern U. mollis (Figs 3 and 4b), traditional linear measurements encompassing the entire cranium did this when taxonomic sampling was limited to just the focal taxa. Linear measurements also separated subspecies idahoensis and artemesiae within the northern mollis lineage (Fig. 4a). Thus, evidence from morphology of the entire cranium supports nuDNA-based delimitation hypotheses presented ...
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... in lengths and widths of the auditory bullae and length of the bony palette (Table 4), with idahoensis larger in each. However, again, there is considerable overlap of combined U. idahoensis with U. mollis in individual measurements of the cranium and dentition. These patterns are evident in the ordinations of cranial morphological data as well (Fig. 4), which reveal nearly complete separation of the 2 subspecies artemesiae and idahoensis along the first component, reflecting the substantial size differences between these taxa but substantial overlap between them on component 2 indicating similarity in shape. In contrast, U. mollis overlaps with both idahoensis and artemesiae on ...
Context 4
... including orbital shelf of frontal, more elevated; upper (superior) face of premaxillary larger and usually reaching farther posteriorly; bullae larger; teeth heavier, the toothrow longer (8.5 mm.)." Most of these characteristics are supported by our analyses based on idahoensis having a generally larger size than U. mollis (component 1 of PCA, Fig. 4). Key traits mentioned by Merriam (1913) that are corroborated here based on component 2 of our PCA are the larger bullae and longer toothrow, although Merriam does not comment on the full length of the bony palate, which was also an important trait for distinguishing U. idahoensis from U. mollis. Merriam (1913) also provided the ...