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Because they do not stop growing, the animal must continue to wear them down so that they do not reach and pierce the skull.
As the incisors grind against each other, the softer dentine on the rear of the teeth wears away, leaving the sharp enamel edge shaped like the blade of a chisel.
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The rodent fossil record dates back to the Paleocene on the supercontinent of Laurasia.
Many have litters of underdeveloped, altricial young, while others are precocial (relatively well developed) at birth.Other animals such as rabbits, hares, and pikas, whose incisors also grow continually, were once included with them, but are now considered to be in a separate order, the Lagomorpha.Nonetheless, Rodentia and Lagomorpha are sister groups, sharing a most recent common ancestor and forming the clade of Glires.Species can be arboreal, fossorial (burrowing), or semiaquatic.Well-known rodents include mice, rats, squirrels, prairie dogs, porcupines, beavers, guinea pigs, hamsters, gerbils and capybaras.