Rodentia is the largest order of all living mammals, and contains approximately 1500 species.
Skull size of R. norvegicus is 4.2 to 4.5 cms and teeth count of 16. Their teeth are characterized by a single pair of upper and lower incisors that are specialized for gnawing, grow continuously throughout their lives . Canines and premolars are absent. Molars, of which there are three each side also grow continuously.
The skeleton, number of vertebrae in the respective regions of the vertebral column. These are, cervical 7 (as in rabbit), thoracic 13 (12 in rabbit), lumber 6 (7 in rabbit), sacral 2 (usually 1 in rabbit), and caudal 26 to 30 (about 18 in rabbit).
Their diet is adaptable, from that of a herbivores to a carnivores as
opportunities present themselves.