Most rodents are small animals with robust bodies, short limbs, and long tails.
Nonetheless, Rodentia and Lagomorpha are sister groups, sharing a most recent common ancestor and forming the clade of Glires.
The Hystricomorpha, such as the guinea pig, have larger superficial masseter muscles and smaller deep masseter muscles than rats or squirrels, possibly making them less efficient at biting with the incisors, but their enlarged internal pterygoid muscles may allow them to move the jaw further sideways when chewing.
The cheek pouch is a specific morphological feature used for storing food and is evident in particular subgroups of rodents like kangaroo rats, hamsters, chipmunks and gophers which have two bags that may range from the mouth to the front of the shoulders.
Mating among rodents can vary from monogamy, to polygyny, to promiscuity.
Many have litters of underdeveloped, altricial young, while others are precocial (relatively well developed) at birth.