Quick Answer: Rodents are a group of mammals belonging to the order Rodentia characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. Rodents make up about 40% of all mammal species. They are native to all major landmasses except Antarctica and several oceanic islands, though they have subsequently been introduced to most of these landmasses by human activity. Most rodents are small animals with robust bodies, short limbs, and long tails. They use their sharp incisors to gnaw food, excavate burrows, and defend themselves. Most eat plant material, but some have more varied diets. Rodents are extremely diverse in their ecology and lifestyles and can be found in almost every terrestrial habitat, including human-made environments. Species can be arboreal, fossorial, saltatorial/ricochetal, or semiaquatic. They tend to be social animals, and many species live in societies with complex ways of communicating with each other.