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)
1.
Zygomatic arch complete, skull flat and broad ---- (Moles) Go to
---------2
Zygomatic arch not complete, skull not flat and
broad --------------
2.
3.
(Shrews) Go
to 3
Upper teeth 10 on each side: mandibular teeth 8 (SE Mole)
Scalopus
each -------------Upper teeth 10 on each side: mandibuIar teeth
11 on each side --------------
(NW Mole)
Scapanus
Skull 1.0 to 1.5cm total length; upper teeth 9 on
each side --------------
(Least Shrew)
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.
Shrew) Blarina
also of the same size; sixth tooth minute and
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 -------------Infraorbital canal not present -------------2. Upper incisors distinctly grooved --------------
Go to 2
Go to 3
(Pocket Mouse)
Perognathus
Upper incisors not distinctly grooved ------------- (Pocket Gopher)
Thomomys
Skull flat and broad; cheek teeth acutely
3. angled and may appear as one continuous
tooth
Skull generally rounded; cheek teeth lobed or
rounded and easily distinguished individually
4. Upper incisors distinctly grooved --------------
(Pine Vole)
Microtus
Go to 4
(Harvest Mouse)
Reithrodontomys
Upper incisors not distinctly grooved ------------Go to 5
5.
Posterior edge of palate ending well beyond
last cheek teeth --------------
Go to 6
Posterior edge of palate ending even with or
slightly beyond last cheek teeth
Go to 8
Upper incisors notched; anterior palatine
6. foramina extend well beyond anterior edge of
cheek teeth
Upper incisors not notched; anterior palatine
foramina do not extend well beyond anterior
edge of cheek teeth -------------7.
(House Mouse)
Mus
Go to 7
Posterior palatine foramina obvious and
(Rice Rat)
located just beyond last cheek teeth -------------- Oryzomys
Posterior palatine formina minute and located
between second pair of cheek teeth
Rat) Rattus
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
sigmoid --------------
(Deer Mouse)
Peromyscus