Eugeneodontida



The Eugeneodontida, sometimes also called Eugeneodontiformes, is an extinct and poorly known order of cartilaginous fishes. They possessed "tooth-whorls" on the symphysis of either the lower or both jaws and pectoral fins supported by long radials. They probably lacked pelvic fins and anal fins. The palatoquadrate was either fused to the skull or reduced. Now determined to be within the Holocephali, their closest living relatives are ratfish. The eugeneodonts are named after paleontologist Eugene S. Richardson, Jr. The Eugeneodontida disappeared in the Early Triassic. The geologically youngest fossils of the group are known from the Sulphur Mountain Formation (western Canada), Vardebukta Formation (Svalbard, Norway) and Wordie Creek Formation (Greenland).

Members of the Eugeneodontida are further classified into different families, the most well-preserved members that have been discovered are commonly placed within the families Helicoprionidae ("spiral saws"), and Edestidae ("those which devour"), the former containing the genera Helicoprion, Sarcoprion, and Parahelicoprion, and the latter containing the genera Edestus, Lestrodus, and Metaxyacanthus. All eugeneodonts are thought to have been obligate carnivores, with each genus having specialized feeding behaviors, territory ranges, and specific prey.

Among the eugeneodonts, some members of the superfamily Edestoidea are probably the largest animals of their time, with the Late Carboniferous Edestus reaching about or exceeding 6.7 m in length, and with the Early Permian Helicoprion measuring over 7.6 m long.

Taxonomy
The list below shows taxa included within Eugeneodontida.
 * Superfamily Caseodontoidea
 * Family Caseodontidae
 * Genus Caseodus
 * Genus Erikodus
 * Genus Fadenia
 * Genus Ornithoprion
 * Genus Pirodus
 * Genus Romerodus
 * Family Eugeneodontidae
 * Genus Bobbodus
 * Genus Eugeneodus
 * Genus Gilliodus
 * Family incertae sedis
 * Genus Campodus
 * Genus Chiastodus
 * Genus Tiaraju
 * Superfamily Edestoidea
 * Family Helicoprionidae
 * Genus Agassizodus
 * Genus Arpagodus
 * Genus Campyloprion
 * Genus Helicoprion
 * Genus Parahelicoprion
 * Genus Sarcoprion
 * Genus Sinohelicoprion
 * Genus Toxoprion
 * Family Edestidae
 * Genus Edestus
 * Genus Helicampodus
 * Genus Lestrodus
 * Genus Parahelicampodus
 * Genus Syntomodus
 * Genus Protopirata
 * Genus Euctenius
 * Genus Prospiraxis
 * Genus Spiraxis
 * Genus Metaxyacanthus
 * Family incertae sedis
 * Genus Paredestus