The Eugeneodontida is an extinct and poorly known order of

cartilaginous fishe Chondrichthyes (; ) is a class (biology), class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed ...

s. They possessed "tooth-whorls" on the

symphysis A symphysis (, pl. symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing togethe ...

of either the lower or both jaws and pectoral fins supported by long radials. They probably lacked pelvic fins and anal fins. The

palatoquadrate In some fishes, the palatoquadrate is the dorsal component of the mandibular arch, the ventral one being Meckel's cartilage. The palatoquadrate forms from splanchnocranium in various chordates including placoderms and acanthodians. See also * ...

was either fused to the skull or reduced. Now determined to be within the

Holocephali Holocephali ("complete heads"), sometimes given the term Euchondrocephali, is a subclass of cartilaginous fish in the class Chondrichthyes. The earliest fossils are of teeth and come from the Devonian period. Little is known about these primitiv ...

, their closest living relatives are

ratfish Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. At o ...

. The eugeneodonts are named after paleontologist Eugene S. Richardson, Jr. The Eugeneodontida disappeared in the

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

. 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 ''Helicoprion'' is an extinct genus of shark-like eugeneodont fish. Almost all fossil specimens are of spirally arranged clusters of the individuals' teeth, called "tooth whorls", which in life were embedded in the lower jaw. As with most extin ...

'', '' Sarcoprion'', and '' Parahelicoprion'', and the latter containing the genera '' Edestus'', ''

Lestrodus ''Lestrodus'' is an extinct genus of edestid fish that lived during the Late Carboniferous. It contains one valid species, ''L. newtoni'', which is known from a single tooth whorl from the Millstone Grit of England. It was originally named as a ...

'', and '' Metaxyacanthus''. All eugeneodonts are thought to have been obligate

carnivores A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other so ...

, with each genus having specialized feeding behaviors, territory ranges, and specific prey.

Taxonomy

*Superfamily Caseodontoidea **Family Caseodontidae ***Genus '' Caseodus'' ***Genus '' Erikodus'' ***Genus '' Fadenia'' ***Genus '' Ornithoprion'' ***Genus '' Pirodus'' ***Genus ''

Romerodus ''Romerodus'' is an extinct genus of eugeneodontid holocephalian from the Carboniferous of North America. Fossils have been found in Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South ...

'' **Family Eugeneodontidae ***Genus '' Bobbodus'' ***Genus '' Eugeneodus'' ***Genus '' Gilliodus'' **Family ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'' ***Genus '' Campodus'' ***Genus '' Chiastodus'' ***Genus '' Tiaraju'' *Superfamily Edestoidea **Family Helicoprionidae ***Genus '' Agassizodus'' ***Genus '' Arpagodus'' ***Genus '' Campyloprion'' ***Genus ''

'' ***Genus '' Parahelicoprion'' ***Genus '' Sarcoprion'' ***Genus '' Toxoprion'' **Family Edestidae ***Genus '' Edestus'' ***Genus '' Helicampodus'' ***Genus ''

'' ***Genus '' Parahelicampodus'' ***Genus '' Syntomodus'' **Family ''

'' ***Genus '' Paredestus''

References

External links

Palaeos Vertebrates 70.100 Chondrichthyes: Eugnathostomata at paleos.com
JSTOR: Journal of Paleontology Vol. 70, No. 1 (Jan., 1996), pp. 162-165
at Devonian Times Eugeneodontida, Mississippian first appearances Mississippian taxonomic orders Pennsylvanian taxonomic orders Cisuralian taxonomic orders Guadalupian taxonomic orders Lopingian taxonomic orders Early Triassic taxonomic orders Early Triassic extinctions Prehistoric cartilaginous fish orders {{paleo-shark-stub