 Spines in mammals include the prickles of hedgehogs and among rodents, the quills of both New World and Old World porcupines as well as the prickly fur of spiny mice, spiny pocket mice and spiny rats.They are also found on afrotherian tenrecs, marsupial spiny bandicoots and on echidnas, of the monotremes.An ancient synapsid, "Dimetrodon", had extremely long spines on its backbone that were joined together with a web of skin that formed a sail-like structure.