2. Have a single pair of continuously growing incisors in both the upper and lower jaws. Have a diastema, or a gap between the incisors and the cheek teeth. 43% of all mammals are rodents There are 30 families, and 1,620 species known worldwide. They are found nearly everywhere because they are extremely adaptable 6 Families in PA Sciuridae, Castoridae, Muridae, Dipodidae, Erethizontidae, Cricetidae

3. First rodents were around 66 million years ago. First direct relatives of modern rodents were 20 million years ago. (beaver) Horned Gopher only horned rodent 2.5 mya

4. Beaver Castor canadensis Largest rodent in North America

5. North American Porcupine Erethizon dorsatum Quills are modified hairs Only predator is the fisher

6. Meadow Jumping Mice Zapus hudsonius Woodland Jumping Mice Napaeozapus insignis

7. Subfamily Arvicolinae (lemmings, voles, and muskrat) Rock Vole Meadow Vole Woodland Vole Southern bog lemming Southern red-backed vole Muskrat Subfamily Neotominae (North American rats/mice) Woodrat Deer mouse White-footed mouse

8. Old world rats and mice 1) House mouse (Mus musculus) 2) Norway rat (Rattus norvegicus) 3) Black Rat (Rattus rattus)

9. Subfamily Sciurinae (tree squirrels and flying squirrels) Gray Squirrel Fox squirrel Red squirrel Northern flying squirrel Southern flying squirrel Squirrels, chipmunks, marmots Subfamily Xerinae (chipmunks and ground squirrels) Woodchuck Eastern Chipmunk Thirteen-lined ground squirrel Found only in Mercer and Venango counties