Chondrichthyes is a 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 of bone tissue. Chondrichthyes are jawed vertebrates with paired fins, paired nares, scales, and a heart with its chambers in series. Extant chondrichthyes range in size from the 10 cm finless sleeper ray to the 10 m whale shark.
Cladoselache is an extinct genus of shark-like chondrichthyan from the Late Devonian (Famennian) of North America. Growing to several meters in length, it is considered to have been a fast-moving and fairly agile marine predator due to its streamlined body and deeply forked tail. Cladoselache is one of the best known of the early chondrichthyans in part due to an abundance of well preserved fossils, discovered in the Cleveland Shale on the south shore of Lake Erie. In addition to the skeleton, the fossils were so well preserved that they included traces of skin, muscle fibers, and internal organs, such as the kidneys.
Orthacanthus is an extinct genus of fresh-water xenacanthid sharks, named by Louis Agassiz in 1836, ranging from the Upper Carboniferous until the Lower Permian. Orthacanthus had a nektobenthic life habitat, with a carnivorous diet. Multiple sources have also discovered evidence of cannibalism in the diet of Orthacanthus and of "filial cannibalism" where adult Orthacanthus preyed upon juvenile Orthacanthus. The genus Orthacanthus has been synonymized with Dittodus, Didymodus, and Diplodus.
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.
Stethacanthus is an extinct genus of shark-like holocephalians which lived from the Late Devonian to Late Carboniferous epoch, dying out around 298.9 million years ago. Fossils have been found in Asia, Europe and North America.
Xenacanthida is an order of prehistoric sharks that appeared during the Lower Carboniferous period. The order includes the families Xenacanthidae, Diplodoselachidae, and Orthacanthidae. The most notable members of the group are the genera Xenacanthus and Orthacanthus. Some Xenacanthida may have grown to lengths of 5 m (16 ft). Most forms had large serrated spines extending backwards from the neck. Xenacanthus had characteristic teeth. Most xenacanths died out at the end of the Permian in the Permian Mass Extinction, with only a few forms surviving into the Triassic period. They were native to freshwater, marginal marine and shallow marine habitats.
Symmoriiformes is an extinct order of holocephalians. Originally named Symmoriida by Zangerl (1981), it has subsequently been known by several other names. Lund (1986) synonymized the group with Cladodontida, while Maisey (2008) corrected the name to Symmoriiformes in order to prevent it from being mistaken for a family. The symmoriiform fossils record appear at the beginning of the Carboniferous. Most of them died out at the start of the Permian, but Dwykaselachus is known from the Artinskian-Kungurian of South Africa. Teeth described from the Valanginian of France and Austria indicate that members of the family Falcatidae might have survived until the Early Cretaceous; however, these teeth were also argued to be more likely neoselachian teeth.
Falcatus is an extinct genus of falcatid chondrichthyan which lived during the early Carboniferous Period in Bear Gulch bay in what is now Montana.
Falcatidae is a family of Paleozoic holocephalians. Members of this family include Falcatus, a small fish from the Bear Gulch Limestone of Montana. The family first appeared around the start of the Carboniferous, and there is some evidence that they survived well into the early Cretaceous, though its putative Cretaceous members were also argued to be more likely neoselachians.
Hybodontiformes, also called hybodonts, are an extinct subset of Elasmobranchii which existed from the late Devonian to the Late Cretaceous. They form the group of sharks closest to neoselachians, the clade of modern sharks and rays. Hybodonts were named and are distinguished based on their conical tooth shape. They comprised the main group of Jurassic sharks in Europe and North America. They survived into the Late Cretaceous before going extinct, possibly due to competition from other sharks. Lonchidion was one of the last hybodonts — its distinctive serrated fine spines occur in freshwater deposits from Wyoming alongside the fossils of the last non-avian dinosaurs, including Tyrannosaurus rex and Triceratops. Hybodontiformes are identified in the fossil record predominantly based on distinct teeth and fin spines. They were known to live in both fresh and salt water environments.
Cardabiodon is an extinct genus of large mackerel shark that lived about 95 to 91 million years ago (Ma) during the Cenomanian to Turonian of the Late Cretaceous. It is a member of the Cardabiodontidae, a family unique among mackerel sharks due to differing dental structures, and contains the two species C. ricki and C. venator. Cardabiodon fossils have been found in Australia, North America, England, and Kazakhstan. It was likely an antitropical shark that inhabited temperate neritic and offshore oceans between 40° and 60° paleolatitude, similar to the modern porbeagle shark.
Cladodus is an extinct genus of cartilaginous fishes in the family Cladoselachidae. As the name implies, they are a type of cladodont, primitive sharks with teeth designed to snag fish and swallow them whole, instead of sawing off chunks to swallow.
Cladodont is the term for a common category of early Devonian shark known primarily for its "multi-cusped" tooth consisting of one long blade surrounded by many short, fork-like tines, designed to catch food that was swallowed whole, instead of being used to saw off chunks of meat like many modern sharks. The skinny teeth would puncture and grasp the prey, keeping it from wriggling free.
Synechodontiformes is an extinct order of prehistoric sharks, known from the Permian to the Paleogene. They are a stem-group of Neoselachii, the group that contains modern sharks and rays. They were previously considered a paraphyletic grouping, but recent studies have recovered the group as monophyletic. Members of the clade are united by two synapomorphies, "pseudopolyaulacorhize tooth root pattern present; labial root depression in basal view present". The oldest possible member of the clade are teeth from the early Permian (Cisuralian) of the Ural Mountains.
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.
Altusmirus is an extinct genus of ground shark from the Early Cretaceous age of Austria. There is only one known species, A. triquetrus, named by Iris Fuchs in 2018. It was related to Fornicatus.
Ctenacanthiformes is an extinct order of chondrichthyan fish. They possessed ornamented fin spines and cladodont dentition. Members of the family Ctenacanthidae may have survived into the Cretaceous based on teeth found in deep water deposits of Valanginian age in France and Austria.
Ctenacanthidae is an extinct family of prehistoric sharks in the order Ctenacanthiformes. Species of the different genera are found in strata ranging from Devonian to Cretaceous, with a worldwide distribution.
Ctenacanthoidea is an extinct superfamily of prehistoric sharks. These nectonic carnivores of actively mobile appeared 407 Ma ago, and managed to survive until the early Cretaceous. Miocene record, Wodnika ocoyae is later considered as concretion. Its distribution is practically worldwide.
Lebachacanthus is a genus of extinct Xenacanthid shark known from the early Permian. During the late Paleozoic, xenacanths ruled the freshwater swamps and bogs of the world, preying on small amphibian-like animals.
