The Hexanchiformes are a primitive order of sharks, numbering just seven extant species in two families. Fossil sharks that were apparently very similar to modern sevengill species are known from Jurassic specimens.
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.
Rajiformes is one of the four orders in the superorder Batoidea, flattened cartilaginous fishes related to sharks. Rajiforms are distinguished by the presence of greatly enlarged pectoral fins, which reach as far forward as the sides of the head, with a generally flattened body. The undulatory pectoral fin motion diagnostic to this taxon is known as rajiform locomotion. The eyes and spiracles are located on the upper surface of the head and the gill slits are on the underside of the body. Most species give birth to live young, although some lay eggs enclosed in a horny capsule.
Sclerorhynchus is an extinct genus of ganopristid sclerorhynchoid that lived during the Late Cretaceous. The genus Ganopristis is considered a junior synonym of Sclerorhynchus. It was a widespread genus, with fossils found in the Middle East, North Africa, Europe, and North America. While it had a long rostrum with large denticles similar to sawfishes and sawsharks, its closest living relatives are actually skates. Complete specimens of S. atavus show that its fin arrangement was similar to skates, with the pectoral and pelvic fins touching, both dorsal fins located behind the pelvic fins, and a reduced caudal fin.
Schizorhiza is an extinct genus of schizorhizid sclerorhynchoid that lived during the Late Cretaceous. It contains one valid species, Schizorhiza stromeri. It lived from the Campanian to Maastrichtian, and its fossils have been found in Africa, the Middle East, North America, and South America.
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.
Onchopristis is an extinct genus of sclerorhynchoid from the Cretaceous of North Africa, Europe, and North America. Its name is derived from the Ancient Greek ónkos and prístis. It contains two valid species, O. numida and O. dunklei, though some researchers argue that both may be considered a single taxon with variation in morphology caused by a wide geographical range. Specimens of Onchopristis have been discovered in coastal and fluvial deposits dated from the Barremian to the Cenomanian age, making this genus one of the oldest and longest-lived sclerorhynchoid genera.
Ptychotrygon is a genus of sawfish-like ray whose fossils have been found worldwide from the Cretaceous period (Albian-Maastrichtian). Along with Ptychotrygonoides, Texatrygon, and Asflapristis, it is the member of the family Ptychotrygonidae within the suborder Sclerorhynchoidei.
Onchosaurus is an extinct genus of sclerorhynchid sawskate from the Late Cretaceous. Its fossils have been found in the Cretaceous sediments of Egypt, Brazil, Congo, Morocco, France, Niger, Japan, Chile, Peru and the United States.
Pseudocorax is an extinct genus of mackerel sharks that lived during the Late Cretaceous. It contains six valid species that have been found in Europe, the Middle East, North Africa, and North America. It was formerly assigned to the family Anacoracidae, but is now placed in its own family Pseudocoracidae along with Galeocorax. The former species "P." australis and "P." primulus have been reidentified as species of Echinorhinus and Squalicorax, respectively.
Pristiorajea is a defunct clade of chondrichthyans containing the sawsharks (Pristiophoriformes) and rays. It is sister to the Squatiniformes and shares a common ancestry with the Squaliformes. However, phylogenetic evidence supports rays and sharks as being monophyletic groupings and distinct from one another.
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.
Paracestracion is an extinct genus of heterodontiform sharks from Early Jurassic to Early Cretaceous-aged rocks of England, France, Germany and Luxembourg. The genus was first described in 1911 by Ernst Hermann Friedrich von Koken in Karl Alfred von Zittel.
Eoptolamna is an extinct genus of mackerel sharks that lived during the Cretaceous. It contains two valid species, E. eccentrolopha and E. supracretacea, which have been found in Europe and North Africa.
Ganopristidae is an extinct family of cartilaginous fish from the Cretaceous belonging to the suborder Sclerorhynchoidei. While the name Sclerorhynchidae is often used for this family, it is a junior synonym of Ganopristidae. This family contains the genera Libanopristis, Micropristis, and Sclerorhynchus. The type genus Ganopristis is considered to be a junior synonym of Sclerorhynchus.
The Sao Khua sclerorhynchoid is an unnamed genus and species of sclerorhynchoid from the Early Cretaceous Sao Khua Formation in Thailand. It is known from the tip of a rostral denticle that is deposited in the Sirindhorn Museum as SM 2012-1-021. The denticle has a single barb similar to Onchopristis, Onchosaurus, and Pucapristis, but is distinguished from all other genera by having a row of enameloid "droplets" on each side. It is one of the earliest sclerorhynchoids, along with Celtipristis and Onchopristis which also appeared in the Barremian.
Galeocorax is an extinct genus of mackerel sharks that lived during the Late Cretaceous. It contains a single valid species, G. jaekeli, that has been found in Europe and North America.
Ptychocorax is an extinct genus of mackerel sharks that lived during the Late Cretaceous. It contains three valid species that have been found in Europe and Asia. It was originally identified as a hybodontiform, but was later reidentified as an anacoracid. It has also been considered to belong to its own family, Ptychocoracidae. Ptychocorax is characterized by its unique dentition, combining Squalicorax-like, cutting anterior teeth with Ptychodus-like, crushing posterior teeth.
Schizorhizidae is an extinct family of cartilaginous fish from the Late Cretaceous belonging to the suborder Sclerorhynchoidei. This family contains the genera Harranahynchus and Schizorhiza. It was originally named as a subfamily of Sclerorhynchidae, but was later raised to the rank of family.
