Xenacanthus

Xenacanthus (from Ancient Greek ξένος, xénos, 'foreign, alien' + ἄκανθος, akanthos, 'spine') is an extinct genus of xenacanth cartilaginous fish. It lived in freshwater environments, and fossils of various species have been found worldwide.

Description
Xenacanthus is relatively small member in its order. X. decheni reached about 1 m, X. meisenheimensis reached up to 1.2 m, X. (Expleuracanthus) gaudryi reached 58 cm. X. parallelus is one of the smallest xenacanth, male reached 20 cm and female reached 34 cm, both are fully grown.

The dorsal fin was ribbonlike and ran the entire length of the back and round the tail, where it joined with the anal fin. This arrangement resembles that of modern conger eels, and Xenacanthus probably swam in a similar manner. A distinctive spine projected from the back of the head and gave the genus its name. The spike has even been speculated to have been venomous, perhaps in a similar manner to a sting ray. The teeth had an unusual "V" shape, and it probably fed on small crustaceans and heavily scaled palaeoniscid fishes. As with many xencanths, Xenacanthus is mainly known because of fossilised teeth and spines.

Fossils are known from the Carboniferous-Permian of North America, Europe, and South America. Triassic species have been moved into the separate genus Mooreodontus.

Species

 * X. texensis
 * X. atriossis
 * X. compressus
 * X. indicus
 * X. decheni
 * X. denticulatus
 * X. erectus
 * X. gibbosus
 * X. gracilis
 * X. howsei
 * X. laevissimus
 * X. latus
 * X. luedernesis
 * X. ossiani
 * X. ovalis
 * X. parallelus
 * X. ragonhai - Rio do Rasto Formation, Brazil
 * X. robustus
 * X. serratus
 * X. slaughteri
 * X. taylori