Key to the Skulls of North Dakota Mammals

1. Three molars on each side of lower jaw.......................................2
   One or two molars on each side of lower jaw..................................7

2. Broad rostrum; upper molar rows parallel.............Ursidae, Ursus americanus
                                                                       Black Bear
   Long narrow rostrum; upper tooth rows not parallel.................Canidae...3

3. Condylobasal length more than 155mm (Fig. 11)................................4
   Condylobasal length less than 155mm..........................................5

4. Condylobasal length usually more than 200mm; greatest length
     of skull usually more than 250mm.................................Canis lupus
                                                                        Grey Wolf
   Condylobasal length usually less than 200mm; greatest length
     of skull usually less than 250mm...............................Canis latrans
                                                                           Coyote

5. Sagittal crest distinctly "U" shaped; ventral margin of lower jaw
     with a very distinct step (Fig. 47).................Urocyon cinereoargenteus
                                                                         Grey Fox
   Sagittal crest with "V" shaped or not as above; ventral margin of lower
     jaw without distinct step (Fig. 48)........................................6

6. Condylobasal length more than 125mm..............................Vulpes vulpes
                                                                          Red Fox
   Condylobasal length less than 125mm...............................Vulpes velox
                                                                        Swift Fox

7. Six upper and six lower molariform teeth............Procyonidae, Procyon lotor
                                                                          Raccoon
   Not as above.................................................................8

8. Three or four upper and three lower molariform teeth...............Felidae...9
   Four or five upper and more than three lower molariform
     teeth........................................................Mustelidae...11

9. Three upper and two lower premolars.............................Felis concolor
                                                                    Mountain Lion
   Two upper and two lower premolars...........................................10

10. Hypoglossal foramen separate from foramen lacerum posterius
      (may be difficult to separate from Bobcat)(Fig. 49)..............Felis lynx
                                                                             Lynx
    Hypoglossal foramen confluent with foramen lacerum
      posterius (Fig. 50).............................................Felis rufus
                                                                           Bobcat

11. Total teeth, 38...............................................Martes pennanti
                                                                           Fisher
    Total teeth less than 38...................................................12

12. Total teeth, 36..............................................Lutra canadensis
                                                                      River Otter
    Total teeth, 34............................................................13

13. Palate not extending much beyond posterior edge of last
      upper molars.............................................................14
    Palate extending appreciably beyond posterior edge of last
      upper molars.............................................................15

14. Condylobasal length less than 60mm.........................Spilogale putorius
                                                            Eastern Spotted Skunk
    Condylobasal length more than 60mm..........................Mephitis mephitis
                                                                    Striped Skunk

15. Greatest length of skull more than 90mm; last molar
      triangular shaped.............................................Taxidea taxus
                                                                           Badger
    Greatest length of skull less than 90mm; last molar dumbbell
      shaped (Mustela — these species may be hard to separate)..................16

16. Condylobasal length less than 55mm.........................................17
    Condylobasal length more than 55mm.........................................18

17. Condylobasal length more than 37mm............................Mustela frenata
                                                               Long-tailed Weasel
    Condylobasal length less than 37mm.........................................19

18. Postorbital process well developed, robust; zygomatic
      breadth more than 40mm.....................................Mustela nigripes
                                                              Black-footed Ferret
    Postorbital process poorly developed, not robust; zygomatic
      breadth less than 40mm.......................................Mustela vision
                                                                             Mink

19. Basilar length of skull less than 31mm (Fig. 51)..............Mustela nivalis
                                                                     Least Weasel
    Basilar length of skull 31mm or longer........................Mustela erminea
                                                                           Ermine