Mammalogy Lab 2: Didelphimorphia and Soricomorpha (opossums, shrews and moles)

Order Didelphimorphia, Family Didelphidae—American opossums Virginia opossum—Didelphis virginiana

1) dental formula = I5/4 C1/1 P3/3 M4/4 2) prominent sagittal crest 3) fenestrated palatines 4) angular process medial from mandible

Didelphis virginiana

•  Up to 25 young in a litter •  2g at birth •  ~ 3 months in the pouch •  ~ 8-9 young emerge

•  Only species in the Didelphidae that ranges north into the US & Canada

•  Omnivorous – insects, beetles, small mammals and birds, grain, berries and fruits, grass, carrion…garbage!

Order Soricomorpha, Family Soricidae—shrews

1) incomplete zygomatic arches 2) at least some teeth tipped with red or black 3) cheek teeth dilambdodont 4) bicuspid I1

Soricidae •  Need to eat every few

hours – very fast metabolism

•  Eat twice their own body weight daily!

•  Rarely live longer than 18 months

•  Several large litters •  Red on teeth is iron –

differential wear creates sharp cutting edges

pygmy shrew—Sorex (Microsorex) hoyi

1) only 3 unicuspids readily visible from side

1 2 4

•  Smaller (1-3g) in southern parts of range •  Larger (4-7g) in Alaska and Northern regions •  Variable habitat – open fields to wooded slope; wet

and dry soils

Sorex hoyi

•  Range across Canada and northern USA

•  Quite rare – abundance underestimated due to trapping methods? (pitfall traps better than typical small mammal traps)

water shrew—Sorex palustris

1) skull length > 19 mm 2) rostrum short, relative to S. bendirii

Pacific water shrew—Sorex bendirii

1) skull length > 19 mm 2) rostrum longer and more downcurved,

relative to S. palustris

Sorex bendirii

Sorex palustris

Adapted for swimming – stiff hairs on feet increase SA for aquatic propulsion.

arctic shrew—Sorex arcticus masked shrew—Sorex cinereus tundra shrew—Sorex tundrensis

1 2 3 4

1) 3rd unicuspid not smaller than 4th

Sorex arcticus

•  Range: most of Canada – NE BC •  Tri-colored pelage – dark back, lighter

sides and venter •  Aquire tricolored

pattern at first Autumn moult, and retain it throughout life

Sorex tundrensis

•  Range: Alaska, NW Canada, and extreme NW BC

•  Summer coat tricolor – winter coat bicolor – retain dark back, sides take on similar light color to venter

Sorex cinereus

•  Range – Alaska, most of Canada and USA

•  Largest distribution of any N American shrew

•  9 subspecies recognised

dusky shrew—Sorex monticolus Trowbridge’s shrew—Sorex trowbridgii

vagrant shrew—Sorex vagrans

1) 3rd unicuspid smaller than 4th

4 3

Sorex monticolus

•  Range – throughout BC; found in Alaska, W Canada and through W USA.

•  Prefers wet areas; willow and alder thickets, grassy stream banks and alpine tundra

Sorex vagrans

•  Range – S BC and W USA •  Found in wet, grassy areas, marshes and

muddy streams

Sorex trowbridgii •  Range: Extreme SW BC; along Pacific coast to California. •  Usually the most common shrew found in forests of the

Pacific NW USA •  Prefers mature forest – avoids wet, marshy soil

•  Has been observed climbing high into Douglas Fir trees!

Order Soricomorpha, Family Talpidae—moles

1) complete zygomatic arches 2) teeth entirely white

Talpidae

•  Fossorial –  reduced eyesight –  no pinnae –  front feet modified

for burrowing –  fur lies either way

shrew-mole—Neurotrichus gibbsii

1) dentition: I3/3 C1/1 P2/2 M3/3 2) auditory bullae incompletely formed

coast mole—Scapanus orarius

1)   dentition: I3/3 C1/1 P4/4 M3/3 2) auditory bullae completely formed 3) skull < 37 mm

coast mole—Scapanus orarius

Townsend’s mole—Scapanus townsendii

1)   dentition: I3/3 C1/1 P4/4 M3/3 (usually) 2) auditory bullae completely formed 3) skull ≥ 37 mm

Townsend’s mole—Scapanus townsendii