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Temporal range: early Palaeocene – Recent
61.7 mya to present
They have four incisors. These keep growing, and must be kept worn down by gnawing (eroding teeth by grinding them on something hard); this is the origin of the name, from the Latin rodere, "to gnaw", and dent, "tooth".
Most rodents are small. Examples of commonly known rodents are mice, rats, chipmunks, and squirrels. Some other small rodents sometimes kept as pets are Guinea pigs, hamsters, and gerbils. Examples of larger rodents are porcupines, beavers, and the largest living rodent, the capybara, which can grow to between 105 and 135 cm (40-55 in) in length, and weigh 35 to 65 kg (75-140 lbs).
Rabbits, hares, and pikas are sometimes called rodents, because they also have teeth that keep growing. But in 1912 biologists decided to put them in a new, separate order, Lagomorpha, because they have two extra incisors in their upper jaw.
There are more families than these. The list includes the more common families.
- Order Rodentia
- Suborder Anumaluromorpha
- Suborder Castorimorpha
- Suborder Hystricomorpha
- Suborder Sciuromorpha
- Suborder Myomorpha