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.
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 extinct cartilaginous fish, the skeleton is mostly unknown. Fossils of Helicoprion are known from a 20 million year timespan during the Permian period from the Artinskian stage of the Cisuralian to the Roadian stage of the Guadalupian. The closest living relatives of Helicoprion are the chimaeras, though their relationship is very distant. The unusual tooth arrangement is thought to have been an adaption for feeding on soft bodied prey, and may have functioned as a deshelling mechanism for hard bodied cephalopods such as nautiloids and ammonoids. In 2013, systematic revision of Helicoprion via morphometric analysis of the tooth whorls found only H. davisii, H. bessonowi and H. ergassaminon to be valid, with some of the larger tooth whorls being outliers.
Xenacanthida is an order or superorder of extinct shark-like chondrichthyans known from the Carboniferous to Triassic. They were native to freshwater, marginal marine and shallow marine habitats. Some xenacanths may have grown to lengths of 5 m (16 ft). Most xenacanths died out at the end of the Permian in the End-Permian Mass Extinction, with only a few forms surviving into the Triassic.
Secodontosaurus is an extinct genus of "pelycosaur" synapsids that lived from between about 285 to 272 million years ago during the Early Permian. Like the well known Dimetrodon, Secodontosaurus is a carnivorous member of the Eupelycosauria family Sphenacodontidae and has a similar tall dorsal sail. However, its skull is long, low, and narrow, with slender jaws that have teeth that are very similar in size and shape—unlike the shorter, deep skull of Dimetrodon, which has large, prominent canine-like teeth in front and smaller slicing teeth further back in its jaws. Its unusual long, narrow jaws suggest that Secodontosaurus may have been specialized for catching fish or for hunting prey that lived or hid in burrows or crevices. Although no complete skeletons are currently known, Secodontosaurus likely ranged from about 2 to 2.7 metres (7–9 ft) in length, weighing up to 110 kilograms (250 lb).
Edestus is an extinct genus of eugeneodontid holocephalian fish known from the Late Carboniferous (Pennsylvanian) of the United Kingdom, Russia, and the United States. Most remains consist of isolated curved blades or "whorls" that are studded with teeth, that in life were situated within the midline of the upper and lower jaws. Edestus is a Greek name derived from the word edeste, in reference to the aberrant quality and size of the species' teeth. The largest species, E. heinrichi, has been conservatively estimated to reach greater than 6.7 m (22 ft) in length, around the size of the largest known great white shark, possibly making it the largest marine predator to have ever existed up to that point.
Rhizodus is an extinct genus of basal, finned tetrapodomorphs. It belonged to Rhizodontida, one of the earliest-diverging tetrapodomorph clades. Two valid species have been described, both of which lived during the Early Carboniferous epoch. The type species R. hibberti is known from the Viséan stage of the United Kingdom, whereas the species R. serpukhovensis is from the Serpukhovian of Russia. Some fossils referred to the genus Rhizodus have also been found in North America.
Anthracosaurus is an extinct genus of embolomere that lived during the Late Carboniferous in what is now Scotland, England, and Ohio. Measuring around 10 ft (3.0 m) long, it was a large, aquatic eel-like predator. It has a robust skull about 40 centimetres (1.3 ft) in length with large teeth in the jaws and on the roof of the mouth. Anthracosaurus probably inhabited swamps, rivers and lakes. Its name is Greek for "coal lizard".
Campodus is an extinct genus of eugeneodont holocephalans from the Carboniferous. Likely one of the earliest and most basal caseodontoids, it can be characterized by its broad, ridge-ornamented crushing teeth made of various types of dentine. The type species, C. agassizianus, was originally described in 1844 based on a small number of teeth from the Namurian of Belgium.
Loxomma is an extinct genus of Loxommatinae and one of the first Carboniferous tetrapods. They were first described in 1862 and further described in 1870 when two more craniums were found. It is mostly associated with the area of the United Kingdom. They share features with modern reptiles as well as with fish. They had 4 paddle-like limbs that they used to swim in lakes, but they breathed air. Their diet consisted mostly of live fish. They are of the family Baphetidae which are distinguished by their keyhole shaped orbits, while Loxomma themselves are distinguished by the unique texture on their skulls, said to be honeycomb-like.
Fadenia is an extinct genus of eugeneodontid holocephalian chondrichthyan from the Carboniferous Period of Missouri, the Permian period of Greenland, and the Early Triassic epoch of British Columbia, Canada.
Caseodus is an extinct genus of eugeneodontid holocephalian from the Carboniferous of the United States and the Early Triassic of Canada. It was of medium size, measuring 1–1.5 m (3.3–4.9 ft) in length.
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 chimaeras. The eugeneodonts are named after paleontologist Eugene S. Richardson, Jr. The group first appeared in the fossil record during the late Mississippian (Serpukhovian). The youngest eugeneodonts are known from the Early Triassic. The geologically youngest fossils of the group are known from the Sulphur Mountain Formation, Vardebukta Formation and Wordie Creek Formation (Greenland).
The Edestidae are a poorly known, extinct family of shark-like eugeneodontid holocephalid cartilaginous fish.
Lissodus is an extinct genus of hybodont. While fossils attributed to this genus are known spanning from the latest Devonian (Famennian) to the very end of the Cretaceous (Maastrichtian), others consider the genus to have a more narrow range, spanning from the Early Triassic to the end of the Early Cretaceous (Albian). Lissodus is often placed in the family Lonchidiidae, though other authors consider it incertae sedis within Hybodontiformes. Lonchidion has often been regarded as synonymous, but many recent authors consider it to be a distinct but closely related genus.
Adamanterpeton is a genus of Edopoid Temnospondyl within the family Cochleosauridae. The type species A. ohioensis was named in 1998 and is currently the only known species within this genus. Adamanterpeton is rare in the Linton vertebrate assemblage, with other amphibians like Sauropleura, Ophiderpeton, and Colosteus being more common. Unlike other Linton vertebrates, Adamanterpeton may have been adapted to a terrestrial lifestyle.
Toxoprion is an extinct genus of eugeneodont holocephalans whose fossils are found in marine strata from the Early Carboniferous until the Late Permian near Eureka, Nevada.
Ornithoprion is a monotypic genus of extinct eugeneodont holocephalan in the family Caseodontidae. The type and only species, O. hertwigi, lived during the Moscovian stage of the Carboniferous, between 315.2 to 307 million years ago, and is known from black shale deposits in what is now the Midwestern United States. The discovery and description of Ornithoprion, performed primarily via radiography, helped clarify the anatomy of the eugeneodonts, a group which were previously known primarily from isolated tooth whorls. The genus derives its name from the elongate, bill-like rostrum and large eyes, which vaguely resemble the features of a bird, while the species name honors Oscar Hertwig. It is known from specimens preserving the skull and anterior portion of the body.
Agassizodus is an extinct genus of eugeneodont holocephalian from the Carboniferous. It belongs to the family Helicoprionidae, which is sometimes called Agassizodontidae. Like other members of its family, it possessed a symphyseal tooth whorl, which was likely present at the tip of the lower jaw and associated with lateral crushing toothplates. The type species, A. variabilis, was originally named Lophodus variabilis until the name "Lophodus" was determined to be preoccupied.
Campyloprion is an extinct genus of large shark-like eugenodont fish. Two species of Campyloprion are known, C. annectans from Texas and New Mexico in United States and C. ivanovi from Russia. The fossils date to the Gzhelian stage, approximately 303.4–298.9 million years ago. There is a small gap in age between the latest Edestus and the first Campyloprion, which suggests that Campyloprion might have evolved to fit into an ecological niche left vacant by the extinction of Edestus. The fact that Campyloprion is older than Helicoprion suggests, but does not prove, that it is a direct ancestor of Helicoprion.
Paredestus is a monotypic genus of extinct eugeneodont holocephalan from the Early Triassic of Canada. The type and only species, P. bricircum represents the last known member of the superfamily Edestoidea and among the last known eugeneodonts. It was named in 2008 based on tooth and jaw material, with the holotype representing the only known specimen.
