Ischnacanthiformes

Ischnacanthus gracilis

• Worldwide

The Ischnacanthiformes are a group of extinct fish from the upper Paleozoic. Scales that are associated with them, date back to the Middle and Late Silurian, the oldest more complete fossils date from the early Devonian of England and Canada. At the end of the Devonian, most forms died out; few, like Acanthodops survived to the Upper Carboniferous.

Features

The Ischnacanthiformes had a longer in comparison to the Climatiiformes and easily assembled body. They owned two dorsal fins, each of which presided over by a fin spine. The spines of Ischnacanthiformes were slim and narrow and usually ranged deep into the body. Their scales were thin. With the exception of the primitive Ischnacanthiformen Uraniacanthus from England to Ischnacanthiformen lacked additional spines between pectoral and ventral fins. The mouth opens onto the edge of the palatoquadrate and Meckel 's cartilage was ossified and with teeth that were firmly grown together with the bone. The Carapace around the shoulder girdle, which is characteristic of the Climatiiformes, missing the Ischnacanthiformes.

Overall, the Ischnacanthiformes are little known, many described species are known only by isolated jaw and tooth spirals. Most Ischnacanthiformes were unspecialized fish that fed on small organisms. Some larger and more sophisticated forms may also hunted larger prey. The largest genus of Ischnacanthiformes, the Xylacanthus found on Spitsbergen was an estimated 2 m long, but is known only by the jaw.

System

The Ischnacanthiformes be counted among the Acanthodii and also called in German " dogfish sharks ." They are probably the sister group of the Acanthodiformes and together with these, the sister group of bony fishes ( Osteichthyes ) or they must be placed in the root group of bony fishes.