Xenacanthus

Xenacanthus is a genus of prehistoric sharks, belonging to the family Xenacanthidae and the order Xenacanthida. The first species of the genus lived in the later Devonian period, and they survived until the end of the Triassic, 202 million years ago. These freshwater species had a long spine at the back of their head. As in all fossil sharks, Xenacanthus is mainly known because of fossilised teeth and spines.

Xenacanths were almost exclusively freshwater inhabitants, and had a long, rearward-pointing fin spine just behind the cranium (the name xenacanth means "strange spine"), diplodont teeth, a slender, eel-like body, an elongate dorsal fin extending along most of the back, and a symmetrical, tapering tail.

From the back of the skull, a long, sharp, movable spine projected. This spine was made of bone. Though bone manufacture is not commonly associated with cartilaginous fishes, it is possible in certain tissues, such as the vertebrae, of certain shark species.

Species

 * Xenacanthus atriossis
 * Xenacanthus compressus
 * Xenacanthus decheni
 * Xenacanthus denticulatus
 * Xenacanthus erectus
 * Xenacanthus gibbosus
 * Xenacanthus gracilis
 * Xenacanthus howsei
 * Xenacanthus laevissimus
 * Xenacanthus latus
 * Xenacanthus luedernesis
 * Xenacanthus moorei
 * Xenacanthus ossiani
 * Xenacanthus ovalis
 * Xenacanthus parallelus
 * Xenacanthus parvidens
 * Xenacanthus robustus
 * Xenacanthus serratus
 * Xenacanthus slaughteri
 * Xenacanthus taylori