Order: Rodentia "To gnaw"

28 families 2,016 species

Rodents represent the largest mammalian order, comprising >43% of all mammals. They are ubiquitous and cosmopolitan. Rodents occur worldwide in every biome and often are found in close association with humans (comensals). Because of this they are particularly important with respect to crop and food damage, and the spread of diseases.

Rodents are found early in the fossil record - - Mid-Jurassic 200+ mya

Rodents have a single pair upper & lower incisors. The incisors are open-rooted and ever-growing.

- anterior side w/ enamel

- posterior side w/out 1 0 0 3 = 16 (22)
                                  1 0 0 3

 

 

Three groupings of rodents are based on the skull structure and jaw musculature

 

Sciuromorph (squirrel-shaped):

Small infraorbital foramen - masseter muscle (mm) originates on rostrum

 

 

Myomorpha (mouse-shaped):

A slightly larger infraorbital foramen than in Sciuromorphs - mm originates on rostrum and goes through the foramen

 

 

 

 

Hystricomorpha (porcupine pine-shaped):  Large infraorbital foramen

 

 

All rodents have one of only two types of lower jaws - 2 suborders

Sciurognathous - simple dentary with insertion ventral to molariform teeth (straight down) (enlarged coronoid process)

Hystricognathous - strongly angular, flange-like, wider - insertion on bony flange of angular process ( angular process is enlarged)

Endangered rodents in Indiana

Plains pocket Gopher (Geomys bursarius)

Allegheny woodrat (Neotoma magister)

Franklin’s ground squirrel (Geomys bursarius)

(Western harvest mouse) (Reithrodontomys megalotis)