Plate 6 (Mus musculus shown) Old World Rats & Mice (Mus musculus shown) B P A L Tubercular vs. Prismatic Teeth Plate 6 Tubercular ** In each of the following plates the upper right molariform toothrow is shown with the anterior-most tooth at the top and the last molar at the bottom of the photo. The buccal surface (adjacent to the cheek) is to the left and the lingual surface (adjacent to the tongue) is to the right. Prismatic cusp pattern in murids, voles and lemmings (note alternating triangles) (Right upper molariform toothrow of Microtus ochrogaster shown) A = anterior, P = posterior, B = buccal surface, L = lingual surface Alternating enamel (white ridges) and dentin (light brown material) maintains occlusal surfaces as the tooth wears down; enamel is much harder than dentin New World Rats & Mice (Peromyscus maniculatus shown)

Plate 7 Inferorbital foramen Southern red-backed vole Abrupt palate - Transverse shelf Inferorbital foramen Southern red-backed vole (Clethrionomys gapperi) Genus Tamias (Tamias amoenus) Inferorbital foramen situated in the Zygomatic plate Plate 7 Palate sloping downward Meadow vole (Microtus pennsylvanicus) Black-tailed prairie dog (Cynomys ludoviscianus) Inferorbital foramen situated in projection on maxillary bone (Tree squirrels, ground squirrels, and prairie dogs)

Plate 8 Western harvest mouse Sagebrush vole (Lemmicus curtatus) 3 lingual projections on last upper molar a Western harvest mouse (Reithrodontomys megalotis) Ventral view of upper grooved incisors Heather vole (Phenocomys intermedius) a b Northern red-backed vole (Clethrionomys gapperi) 4 lingual projections on last upper molar Plate 8 Northern bog lemming (Synaptomys borealis) Very deep reentrant angles: (a) upper teeth cut inward from buccal surface, (b) lower teeth cut inward from lingual surface b Reentrant angles of both upper (a) and lower (b) molariform teeth much deeper on lingual surface than on buccal surface Prairie vole (Microtus ochrogaster) Reentrant angles of upper molariform teeth equal on lingual and buccal surfaces

Plate 9 Montane vole (Microtus montanus) Meadow vole (Microtus Incisive foramina constrict abruptly and narrow posteriorly (bracket) M2 Meadow vole (Microtus pennsylvanicus) M2 4 closed triangles and posterior loop (arrow) loop Long-tailed vole (Microtus longicaudus) incisive foramina parallel throughout, only slighlty narrower posteriorly M3 Plate 9 M3 with 2 deep reentrant angles on lingual side Water vole (Microtus richardsoni) P4 M1 M3 M2 Red squirrel (Tamiasciurus hudsonicus) Anterior marginof orbit opposite P4 (arrow) M3 with 3 deep reentrant angles on lingual side; no loop on M2 Montane vole (Microtus montanus)

P3 P4 M1 M2 M3 Golden-mantled ground squirrel (Spermophilus lateralis) Columbian ground squirrel (Spermophilus columbianus) The thirteen-lined ground squirrel (S. tridecemlineatus) has similar characteristics; these two species can be separated by greatest length [GL] (SPCO > 45mm, SPTR < 45mm) Plate 10 Higher power Higher power Pronounced anterior valley on P4 - M3 passes completely across the tooth (arrows) Anterior valley on P4 - M3 does not pass completely across the tooth (arrows) Ridge of enamel rises up at lingual side of cusp No ridge of enamel rises up at lingual side of cusp