The Eugeneodontiformes, (also called Eugeneodontida) is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

and poorly known

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

of cartilaginous fishes. They possessed "tooth-whorls" on the

symphysis A symphysis (, : 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 together o ...

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

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

s and anal fins. The palatoquadrate was either fused to the skull or reduced. Now determined to be within the

Holocephali Holocephali (Sometimes spelled Holocephala; Romanization of Greek, Greek for "complete head" in reference to the fusion of Palatoquadrate, upper jaw with the rest of the skull) is a Subclass (biology), subclass of Chondrichthyes, cartilaginous fi ...

, their closest living relatives are

chimaeras Chimaeras are Chondrichthyes, cartilaginous fish in the order (biology), order Chimaeriformes (), known informally as ghost sharks, rat fish (not to be confused with rattails), spookfish, or rabbit fish; the last two names are also applied to B ...

. The eugeneodonts are named after paleontologist Eugene S. Richardson, Jr. The group first appeared in the fossil record during the late Mississippian (

Serpukhovian The Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from Ma to Ma. It is preceded by the Visean and is followed ...

). The youngest eugeneodonts are known from 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 251.9 Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which ...

. The geologically youngest fossils of the group are known from the Sulphur Mountain Formation (western Canada), Vardebukta Formation (

Svalbard Svalbard ( , ), previously known as Spitsbergen or Spitzbergen, is a Norway, Norwegian archipelago that lies at the convergence of the Arctic Ocean with the Atlantic Ocean. North of continental Europe, mainland Europe, it lies about midway be ...

, Norway) and

Wordie Creek Formation The Wordie Creek Formation is an uppermost Permian and Lower Triassic geologic formation in Greenland, outcrops of which are located in Northeast Greenland National Park (until 2008 Tunu County, Danish: Østgrønland, English: East Greenland). ...

(Greenland). Members of the Eugeneodontiformes 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 Extinction, extinct genus of shark-like Chondrichthyes, cartilaginous fish in the order Eugeneodontiformes. Almost all ''Helicoprion'' Fossil, fossils consist of spirally-arranged clusters of fused teeth, called "tooth whor ...

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

Edestus ''Edestus'' is an extinct genus of Eugeneodontida, eugeneodontid holocephalian fish known from the Late Carboniferous (Pennsylvanian (geology), Pennsylvanian) of the United Kingdom, Russia, and the United States. Most remains consist of isolated c ...

'', '' Lestrodus'', 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 nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...

, 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 marine animals of their time, with the

Late Carboniferous Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * Late (The 77s album), ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudo ...

'' estimated to reach about or exceeding in length, with some

Early Permian 01 or 01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * '01 (Richard Müller album), ''01'' (Richard Müller album), 2001 * 01 (Urban Zakapa album), ''01'' (Urban Zakapa album), 2011 * ''01011 ...

'' suggested to be over long by some estimates (though the body length estimates for both genera are somewhat speculative due to both only being known from skull material).

Taxonomy

The list below shows

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

included within Eugeneodontida. *Superfamily

Caseodontoidea The Eugeneodontiformes, (also called Eugeneodontida) is an extinct and poorly known order (biology), order of Chondrichthyes, cartilaginous fishes. They possessed "tooth-whorls" on the symphysis of either the lower or both jaws and pectoral fins ...

**Family Caseodontidae ***Genus '' Caseodus'' ***Genus '' Erikodus'' ***Genus ''

Fadenia ''Fadenia'' is an extinct genus of eugeneodontid holocephalian chondrichthyan from the Carboniferous Period of Missouri (United States), the Permian period of Greenland, and the Early Triassic epoch of British Columbia, Canada ( Sulphur Mount ...

'' ***Genus ''

Ornithoprion ''Ornithoprion'' is an extinct genus of cartilaginous fish. The only species, O. ''hertwigi'', lived during the Moscovian stage of the Pennsylvanian, between 315.2 and 307 million years ago, and is preserved in black shales from what is now t ...

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

incertae sedis or is a term used for a taxonomy (biology), 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, uncertainty ...

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

'' ***Genus '' Parahelicoprion'' ***Genus '' Sarcoprion'' ***Genus '' Sinohelicoprion'' ***Genus '' Toxoprion'' **Family Edestidae ***Genus ''

'' ***Genus '' Helicampodus'' ***Genus '' Lestrodus'' ***Genus '' Parahelicampodus'' ***Genus '' Syntomodus'' ***Genus '' Protopirata'' ***Genus '' Euctenius'' ***Genus '' Prospiraxis'' ***Genus '' Spiraxis'' ***Genus '' Metaxyacanthus'' **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-holocephalan-stub