HIERARCHICAL TAXONOMY OF THE ACANTHODII

SYSTEMATIC BIOLOGY
CLASS ACANTHODII+

Acanthodii (a-kan-THO-de-i) is derived from the Greek root acantha (Ακανθα), which refers to a spine. The reference is to the spines at the anterior of each of the body fins.

Commonly called spiny sharks, acanthodians had numerous fins (both in-line and paired), most of which were supported at the anterior end by a large spine. They were basal gnathostomes that shared a suite of characters with the Osteichthyes and the Chondrichthyes (e.g. gills covered by an operculum, placoid-like scales, etc.). They were small fish but could be as large as 2 meters. That most of them had large eyes suggests that they lived at great depth. By and large, they were lightly armored, and most were toothless.

Although acanthodians have long been considered sisters or precursors to the Chondrichthyes (Janvier 1996), Wilson et al. (2007) and Benton (2005) consider the acanthodians to be sisters to the Osteichthyes. Indeed, they suggest that the distinctions between the two groups might be arbitrary and that the acanthodians are paraphyletic with regard to the bony fishes.

HIERARCHICAL TAXONOMY OF THE CLASS ACANTHODII+. The following descriptions come from Benton (2005) and Nelson (2006). The structure of the following system is also based, in part, on the phylogenetic treatment by Mikko's Phylogeny Web (from the Finnish Museum of Natural History). Taxa in red are extinct.

Drawing of acanthodians from: http://vivaldi.zool.gu.se/Fiskfysiologi_2001/Course_material/Introduction_fish_evolution/Images/Acanthodians.gif

CLASS ACANTHODII+

These were small fish that were lightly armored. They had numerous in-line fins (upper and lower). In addition, they had paired pectoral fins and paired rows of spines that supported fins. The scales that covered the fish were of bone and dentine and showed concentric growth rings. Generally, acanthodians were toothless, though they may have taken whole prey that were secured by back-pointed gill rakers. Most had very large eyes and may have occupied deep water.

Upper Ordovician to the Upper Permian

ORDER CLIMATIIFORMES

Dermal bone with ornamentation in shoulder region; two dorsal fins; each supported by a spine; numerous (up to 6) paired spines between pectoral and pelvic girdles. Teeth absent; or present but not fused to the jaws.

Mid Silurian to Pennsylvanian (North and South America, Greenland, Europe, Asia, Australia, Antarctica).

FAMILY CLIMATIIDAE

Brachycanthus, Climatius, Parexus, Vernicomacanthus.

FAMILY CULMACANTHIDAE

Culmacanthus.

FAMILY DIPLACANTHIDAE

Diplacanthus, Gladiobrachus,Uraniacanthus, Tetranopsyrus.

FAMILY GYRACANTHIDAE

Gyracanthides.

FAMILY EUTHACANTHIDAE

Euthacanthus.

Incertae Sedis: Nostolepis.

ORDER ACANTHODIFORMES

One dorsal fin with spine; no teeth; gill rakers well developed, likely for filter-feeding; prepelvic spines absent.

Lower Devonian to lower Permian ( North America , Europe , Asia , South Africa , Australia , Antarctica ).

FAMILY MESACANTHIDAE

Mesacanthus, Melanoacanthus.

FAMILY CHEIRACANTHIDAE

Carycinacanthus, Cheiracanthus, Homalacanthus.

FAMILY ACANTHODIDAE

Acanthodes, Acanthodopsis, Howittacanthus, Traquairichthys.

ORDER ISCHNACANTHIFORMES

Two dorsal fins, each with a spine; teeth firmly attached to bony jaws; no prepelvic spines.

Upper Silurian to Pennsylvanian (North and South America , Europe , Australia , Antarctica , Asia ).

FAMILY ISHNACANTHIDAE

Atopacacanthus, Ishnacanthus, Marsdenius, Xylacanthus.

FAMILY PORACANTHODIDAE

Poracanthodes.