Porcupine—rodents covered in quills. This grouping is polyphyletic, meaning that different kinds of rodents which are called "porcupines" evolved quills independently through convergent evolution and do not otherwise share a common ancestor that was also a porcupine. In particular, New World porcupines are more closely related to cavies (including capybaras and guinea pigs) than they are to Old World porcupines. All these rodents do share a common ancestor without quills in the suborder Hystricomorpha, whose name means "porcupine-formed," but none of its descendants without quills are themselves considered porcupines. No porcupines are closely related to hedgehogs, which are non-rodent mammals, and are even less closely related to echidnas, which are egg-laying mammals.
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