Dichotomous Key Dichotomous Key Skulls of by MikeJenny


									                              Dichotomous Key
             Skulls of Small Mammals Found in Barn Owl Pellets

  SC. 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
             ----------                                         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)
             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)
             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
           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 --------------
     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
     Skull generally rounded; cheek teeth lobed or
                                                        Go to 4
     rounded and easily distinguished individually
                                                        (Harvest Mouse)
4. Upper incisors distinctly grooved --------------
     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
   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)
     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
   cheek teeth sigmoid or "S" Shaped --------------
     Zygomatic plate not undercut; cheek teeth not      (Deer Mouse)
     sigmoid --------------                             Peromyscus

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