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Mammalogy Lab Order: Rodentia Notes


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Mammalogy Lab
Order: Rodentia
Notes:

  1. Be familiar with skull characteristics (fig 23.2) and jaw conditions (fig 23.3) that are used in keying specimens

  2. *know to species, # know to family/subfamily


General characteristics:

  • Rodentia comprises about 43% of all mammal species

  • Occur in most environments, important invasive species and important zoonotic disease vectors (hanta virus, etc.)

  • Upper and lower incisors arc-shaped, chisel edged, ever growing

  • Anterior surface of incisors is enamel, posterior surface is dentine- maintains sharpness of incisors through differential wear

  • Large diastema present between incisors and cheekteeth

  • 4 basic cranial/muscular conditions based on masseter muscle complex: Protrogomorph, Sciuromorph, Myomorph, and Hystricomorph

  • 2 suborders are based on the jaw condition: Sciuromorpha and Hystricognathi, see figures 23.7 and 23.8 in the lab manual for diagram


Suborder Sciuromorpha (sometimes seen as Sciurognathi)
Family Aplodontidae

* Aplodontia rufa mountain beaver



  • One genus, one species (endemic to Pacific northwest)

  • Skull flattened, greatly widened posteriorly

  • Most primitive living rodent, kidneys incapable of producing concentrated urine, restricted to wet areas

Family Castoridae Beavers

* Castor canadensis



  • Distinct depression in basioccipital

  • Massive mandible, flattened tail, webbed hindfeet, infraorbital canal very small, slit like

  • Dental formula: 1/1 0/0 1/1 3/3

  • Largest rodent in N.A.


Family Sciuridae Squirrels, Chipmunks, Marmots

  • Postorbital process large, auditory bulla not flask-like

  • Zygomatic plate present, infraorbital foramen very small, slit-like

# Marmota broweri

Arctic marmot

Brooks Range,

# Marmota caligata

Hoary marmot

Mottled fur, black face and feet, large size; common in Denali

*Marmota monax

Woodchuck or ground hog

Wide distribution in NA

*Spermophilus parryii

Arctic ground squirrel

Reddish brown, freckled with white spots

*Tamiasciurus hudsonicus

Red squirrel

Common AK sp, small

*Glaucomys sabrinus

Northern flying squirrel

Gliding membrane

Know to family



# Sciurus carlolinensis

Eastern gray squirrel




# Tamias striatus

Eastern chipmunk




# Sciurus niger

Fox squirrel






Family Muridae Mice and Rats

  • 17 Subfamilies, distributed worldwide with few exceptions

  • Infraorbital foramen medium sized, usually V-shaped

  • Dental formula: 1/1 0/0 0/0 2-3/2-3

  • Species often differentiated by dentition: remember lingual = tongue side, labial = cheek side

  • Lemmings tend to have shorter tails than voles, lemmings show blade-like thumbnails

Subfamily Murinae Old World Rats and Mice

# Mus musculus house mouse

* Rattus norvegicus Norway rat

  • Introduced species, scaly tail upper incisors notched in side view, M1 longer than M2 and M3


Subfamily Arvicolinae Voles, Lemmings and Muskrat

Note dentition of Micotus miurus, Microtus oeconomus on handout key



* Clethrionomys rutilus

Northern red-backed vole

Reddish back, palatal bridge incomplete

* Dicrostonyx groenlandicus

Collared lemming

Seasonal pelage change

* Lemmus trimucronatus

Brown lemming

Large, tail short, dark dorsal line, round nose, long hair

* Microtus miurus

Singing vole

M1 usually with 6 closed triangles between the 2 terminal loops and small labial triangle, interorbital area depressed

* Microtus oeconomus

Tundra vole

Can be quite large, M1 with 4 closed triangles, 5th usually confluent with anterior loop

* Microtus xanthognathus

Yellow cheeked vole

Yellow cheek patches, large

* Ondatra zibethicus

Muskrat

Large, >30cm, flattened paddle-like tail


Subfamily Sigmodontinae New World Rats and Mice
# Neotoma magister Allegheny wood rat

# Peromyscus maniculatus Deer Mouse



  • 57 subspecies, variable morphology, widespread in NA

  • Bi-colored, bulging black eyes, naked ears


Family Dipodidae Meadow Jumping mouse

  • Primarily nocturnal, long tailed, can leap up to 3 meters, some are hibernators, hind feet enlarged

* Zapus hudsonius - found in interior AK
Suborder Hystricognathi

Family Erethizontidae New World Porcupines

  • Large infraorbital foramen, blocky skull

  • Crowns of cheekteeth flat, hystricomorph masseter condition

  • Barbed spines

* Erithizon dorsatum Porcupine
Family Myocastoridae Nutria

  • Infraorbital canal very large, w/o distinct groove for nerve passage

  • Angular process strongly deflected outward

* Myocastor coypus Nutria or “mouse beaver”

  • Native to S. America, introduced to NA and Europe

  • Looks like muskrat but with long, round, sparsely furred tail


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