Dichotomous Key Dichotomous Key Skulls of by MikeJenny

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									                              Dichotomous Key
             Skulls of Small Mammals Found in Barn Owl Pellets

  SC.08.07.02.01 Investigates how scientists use taxonomic systems to classify organisms
                                (CMCS 3.1) (CAS 4.2.1)




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1. No gap (diastema) between incisors and cheek teeth: Go to Order Insectivora
(Moles and shrews); go to key below.
2. Gap (diastema) between incisors and cheek teeth: Go to Order Rodentia (Rats,
voles, and mice); go to key below.

Order insectivora (Moles and shrews)

             Zygomatic arch complete, skull flat and broad ---- (Moles) Go to
        1.
             ----------                                         2
             Zygomatic arch not complete, skull not flat and     (Shrews) Go
             broad --------------                                to 3
             Upper teeth 10 on each side: mandibular teeth 8 (SE Mole)
        2.
             each --------------                             Scalopus
             Upper teeth 10 on each side: mandibuIar teeth       (NW Mole)
             11 on each side --------------                      Scapanus
             Skull 1.0 to 1.5cm total length; upper teeth 9 on   (Least Shrew)
        3.
             each side --------------                            Cryptotis
             Skull greater than 1.5cm total length; upper teeth
                                                                Go to 4
             10 on each side --------------
           Skull robust; second and third teeth of same size
           and larger than fourth and fifth teeth which are  (Short Tailed
        4.
           also of the same size; sixth tooth minute and     Shrew) Blarina
           hidden from lateral view --------------
             Skull delicate; second through fifth teeth not
             distinctly paired by size but almost uniform; sixth
                                                                    Shrew) Sorex
             minute but clearly visible from lateral view ---------
             -----

Order rodentia (Rats, voles, and mice)
1. Infraorbital canal present --------------            Go to 2
     Infraorbital canal not present --------------      Go to 3
                                                        (Pocket Mouse)
2. Upper incisors distinctly grooved --------------
                                                        Perognathus
     Upper incisors not distinctly grooved ------------- (Pocket Gopher)
     -                                                   Thomomys
   Skull flat and broad; cheek teeth acutely
                                                        (Pine Vole)
3. angled and may appear as one continuous
                                                        Microtus
   tooth
     Skull generally rounded; cheek teeth lobed or
                                                        Go to 4
     rounded and easily distinguished individually
                                                        (Harvest Mouse)
4. Upper incisors distinctly grooved --------------
                                                        Reithrodontomys
     Upper incisors not distinctly grooved -------------
                                                         Go to 5
     -
     Posterior edge of palate ending well beyond
5.                                                      Go to 6
     last cheek teeth --------------
     Posterior edge of palate ending even with or
                                                        Go to 8
     slightly beyond last cheek teeth
   Upper incisors notched; anterior palatine
                                                        (House Mouse)
6. foramina extend well beyond anterior edge of
                                                        Mus
   cheek teeth
     Upper incisors not notched; anterior palatine
     foramina do not extend well beyond anterior        Go to 7
     edge of cheek teeth --------------
     Posterior palatine foramina obvious and             (Rice Rat)
7.
     located just beyond last cheek teeth -------------- Oryzomys
     Posterior palatine formina minute and located
                                                        Rat) Rattus
     between second pair of cheek teeth
   Zygomatic plate undercut and having a distinct
                                                    (Cotton Rat)
8. dorsal protrusion; second and third pair of
                                                    Sigmodon
   cheek teeth sigmoid or "S" Shaped --------------
     Zygomatic plate not undercut; cheek teeth not      (Deer Mouse)
     sigmoid --------------                             Peromyscus

								
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