Mammalogy Lab Order: Rodentia Notes

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Mammalogy Lab
Order: Rodentia
Notes:

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

# 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

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, 5^th 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

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

* Erithizon dorsatum Porcupine
Family Myocastoridae Nutria

* Myocastor coypus Nutria or “mouse beaver”