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 4 1 2 1) only 3 unicuspids readily visible from side Sorex hoyi • 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 • 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 palustris Adapted for swimming – stiff hairs on feet increase SA for aquatic propulsion. Sorex bendirii arctic shrew—Sorex arcticus masked shrew—Sorex cinereus tundra shrew—Sorex tundrensis 3 4 1 2 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 4 3 1) 3rd unicuspid smaller than 4th 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 .