Chondrichthyes is a class of jawed fish that contains the cartilaginous fish or chondrichthyians, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or bony fish, which have skeletons primarily composed of bone tissue. Chondrichthyes are aquatic vertebrates with paired fins, paired nares, placoid scales, conus arteriosus in the heart, and a lack of opecula and swim bladders. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.
Gnathostomata are the jawed vertebrates. Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates, including humans. In addition to opposing jaws, living gnathostomes have true teeth, paired appendages, the elastomeric protein of elastin, and a horizontal semicircular canal of the inner ear, along with physiological and cellular anatomical characters such as the myelin sheaths of neurons, and an adaptive immune system that has the discrete lymphoid organs of spleen and thymus, and uses V(D)J recombination to create antigen recognition sites, rather than using genetic recombination in the variable lymphocyte receptor gene.
Elasmobranchii is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks, rays, skates, and sawfish. Members of this subclass are characterised by having five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades. The pelvic fins in males are modified to create claspers for the transfer of sperm. There is no swim bladder; instead, these fish maintain buoyancy with large livers rich in oil.
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.
Hybodus is an extinct genus of hybodont, a group of shark-like euselachians that lived from the Late Devonian to the end of the Cretaceous. Species closely related to the type species Hybodus reticulatus lived during the Early Jurassic epoch. Numerous species have been assigned to Hybodus spanning a large period of time, and it is currently considered a wastebasket taxon that is 'broadly polyphyletic' and requires reexamination.
Hybodontiformes, commonly called hybodonts, are an extinct group of shark-like cartilaginous fish (chondrichthyans) which existed from the late Devonian to the Late Cretaceous. Hybodonts share a close common ancestry with modern sharks and rays (Neoselachii) as part of the clade Euselachii. They are distinguished from other chondrichthyans by their distinctive fin spines and cephalic spines present on the heads of males. An ecologically diverse group, they were abundant in marine and freshwater environments during the late Paleozoic and early Mesozoic, but were rare in open marine environments by the end of the Jurassic, having been largely replaced by modern sharks, though they were still common in freshwater and marginal marine habitats. They survived until the end of the Cretaceous, before going extinct.
Anacoracidae is a family of extinct mackerel sharks that lived during the Cretaceous. It includes four valid genera: Nanocorax, Ptychocorax, Scindocorax, and Squalicorax. Two previously-included genera, Galeocorax and Pseudocorax, were reassigned to the family Pseudocoracidae.
Duffinselache is an extinct genus of basal selachimorph elasmobranchii cartilaginous fish known from the Late Triassic of England. It was first named by Duffin in 1998 as a species of Polyacrodus. Plamen S. Andreev and Gilles Cuny in 2012 reassigned to its own genus, and its type species is Duffinselache holwellensis.
This list of fossil fish species is a list of taxa of fish that have been described during the year 2012. The list only includes taxa at the level of genus or species.
Palaeospinax is an extinct genus of synechodontiform cartilaginous fish. Although several species have been described, the genus is considered nomen dubium because the type-specimen of the type species, Palaeospinax priscus, from the Late Triassic-Early Jurassic of Europe lacks appropriate diagnostic characters to define the genus.
This list of fossil fishes described in 2014 is a list of new taxa of placoderms, fossil cartilaginous fishes and bony fishess of every kind that have been described during the year 2014, as well as other significant discoveries and events related to paleontology of fishes that occurred in the year 2014. The list only includes taxa at the level of genus or species.
This list of fossil fishes described in 2013 is a list of new taxa of placoderms, fossil cartilaginous fishes and bony fishess of every kind that have been described during the year 2013. The list only includes taxa at the level of genus or species.
This list of fossil fishes described in 2016 is a list of new taxa of jawless vertebrates, placoderms, acanthodians, fossil cartilaginous fishes, bony fishes and other fishes of every kind that have been described during the year 2016, as well as other significant discoveries and events related to paleontology of fishes that occurred in the year 2016. The list only includes taxa at the level of genus or species.
Synechodontiformes is an extinct order of prehistoric shark-like cartilaginous fish, known from the Permian to the Paleogene. They are considered to be members of Neoselachii, the group that contains modern sharks and rays.
This list of fossil fish described in 2018 is a list of new taxa of jawless vertebrates, placoderms, acanthodians, fossil cartilaginous fish, bony fish, and other fish of every kind that are scheduled to be described during the year 2018, as well as other significant discoveries and events related to paleontology of fish that are scheduled to occur in 2018.
Synechodus is an extinct genus of shark belonging to the family Palaeospinacidae and order Synechodontiformes. It is known from 16 species primarily spanning from the Late Triassic to Paleocene. The dentition is multicusped and was used for grasping. Several species are known from skeletal remains, including the species Synechodus ungeri from the Late Jurassic of Germany, which shows that it was relatively short with large pectoral fins and a proportionally large head with a round snout. This species is suggested to have reached a body length of 30–40 centimetres (0.98–1.31 ft). Skeletal remains are also known of the species Synechodus dubrisiensis from the Cretaceous of Europe. A skeleton of an indeterminate species is also known from the Early Cretaceous (Albian) of France, with a body length of around 70 centimetres (2.3 ft). Synechodus is suggested to have had two dorsal fins that lacked fin spines, though the number of dorsal fins is unknown in Synechodus ungeri.
Pseudorhina is an extinct genus of stem angel shark seemingly restricted to the Mesozoic of Europe. It is represented by several articulated individuals as well as isolated teeth. There are currently four species.
Rhomphaiodon is an extinct genus of prehistoric sharks in the order Synechodontiformes that has been found in Late Triassic and Early Jurassic deposits located in Europe. The type species R. minor was originally named as a species of Hybodus in 1837 by Louis Agassiz. A second species, R. nicolensis, was added when the genus was named in 1993.
Anachronistidae is an extinct family of cartilaginous fish, known from the Carboniferous and Permian periods. They are considered to be the oldest known members of Neoselachii, with a close relationship to modern sharks and rays. They are known from isolated teeth.
