Diplacanthus tenuistriathus Diplacanthus longispinus Diplacanthus crassisimus

Cheiracanthus murchisoni Cheiracanthus latus   Mesacanthus pussilus

Acanthodians

These mostly small fish appeared in the Silurian period. They were very diverse in the Devonian and disappeared in the end of the Permian Period. They can be distinguished from the other fishes by their bony often ornamented spines supporting the fin web of the fins. There are still some questions about their relationship to the other fishes. Real fossil sharks have been found, also having spiny structures but these defence structures have been “invented” several times in the long evolution of the fishes.

In some acanthodians not all the spines probably supported a fin web. They may have been there just to make them les attractive for predators.

The acanthodians have a shagreen of many tiny bony scales often no more than 0.5 mm in length. The outer surface of the scale, the scale crown, is sometimes flat but more often has a specific ribbed structure which makes identification possible. Also in stratigraphic correlation of different sedimentary units, these scales with their different morphology and histology are important markers.

Most of the acanthodians were probably filter feeders although examples are found having well developed jaws with teeth.

Bibliography