Question: what is the difference between an old world porcupine and a new world porcupine?
Answer: The quills, or spines, take various forms depending on the species, but all are modified hairs embedded in skin musculature. Old World porcupines (Hystricidae) have quills embedded in clusters, whereas in New World porcupines (Erethizontidae) single quills are interspersed with bristles, underfur, and hair.