nosky (2000). That possibility was based on one isolated m3 (UCMP 158080) from level 7. This tooth, although superficially similar to Dipodomys lower third molars, is substantially larger (length 1.4 mm, posterior width 1.3 mm, anterior width 0.9 mm) than in D. ordii or D. microps. It compares favorably with Geomys bursarius in overall morphology, but it is slightly smaller and has enamel all the way around the occlusal surface, whereas G. bursarius has dentine tracts. A p4 (UCMP 158081) from the same level also resembles G. bursarius, except for much smaller size and a slightly more antero-posteriorly compressed anterior loph. In these respects the tooth closely resembles Pliogeomys; however, the Porcupine Cave specimens are unrooted and hence cannot be assigned to that genus. The separation between the anterior and posterior lophs is too pronounced and the anterior loph too rounded to be Dipodomys. Given the occurrence of the p4 and m3 in the same level, and their resemblance to Geomys, it seems likely that they indicate a related geomyoid; however, there are several geomyoid genera, including Cratogeomys, Nerterogeomys, and Geomys, which share similar p4 and m3 morphology and are distinguished by characters of skull and jaw morphology. Unfortunately, only these two isolated cheek teeth record the presence of this geomyoid species. Therefore, the material is presently considered nondiagnostic at the generic level, but it does indicate the presence of a geomyoid rodent other than Thomomys.
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