Most numerous of all mammals, rodents comprise more than 1/2 of the living species today and are found on every continent. They have two knawing teeth, or incisors, in both jaws, that are constantly growing. Some are brightly colored and are ground down by constant gnawing. Rodents are plantigrade mammals. They have five digits, although the "thumb" may be inconspicuous, and the hind feet have either five or three digits.