Elasmobranchii

Sharks are a group of elasmobranch cartilaginous fishes characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the division Selachii and are the sister group to the Batomorphi (rays and skates). Some sources extend the term "shark" as an informal category including extinct members of Chondrichthyes (cartilaginous fish) with a shark-like morphology, such as hybodonts. Shark-like chondrichthyans such as Cladoselache and Doliodus first appeared in the Devonian Period (4

Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks (division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by having five to seven pairs of gill slits 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

thumb|left|Life reconstruction of Protospinax annectans Protospinax is an extinct genus of cartilaginous fish from the Middle to Late Jurassic of Europe and Russia. The type species, P. annectans, was found in the Solnhofen limestones of southern Bavaria. Formerly known from only two specimens, further museum specimens of P. annectans were discovered at the Museum of Comparative Zoology of Harvard University in the 1990s, having been misidentified as Squatina and Heterodontus. Six more species, all known only from isolated teeth, have been assigned to Protospinax, though only four including th

Sphenacanthus (from , 'wedge' and , 'spine') is an extinct genus of a chondrichtyan xenacanthiform that belongs to the Sphenacanthidae family and lived from the Late Devonian, through Carboniferous until the Late Permian period in Scotland, Spain, Russia and Brazil. It lived 359 million years ago, and probably it was one of the first member of the elasmobranchians, the lineage that leads to the modern sharks. Sphenacanthus probably hunted small fishes and, unlike their modern-day relatives, it inhabited fresh water lagoons. Sphenacanthus had seven fins, two in the upper part and five in the un

Tristychius (from , 'three' and 'row') is an extinct genus of euselachian chondrichthyan from the Carboniferous period (Visean). Fossils of T. arcuatus, the type and only species, including fin spines have been found in Scotland.

Wodnika is an extinct genus of cartilaginous fish which lived in the Late Permian period in the present area of Germany and Russia. It measured about 1 m (3.2 ft) in length and its tail shape indicates it was probably a good swimmer. Internally, the cartilage skeleton is preserved on the fossil, which is fairly rare for fossilized shark-like chondrichthyans.

Bandringa is an extinct genus of elasmobranch known from the Pennsylvanian subperiod of the Carboniferous period. There is currently a single known species, B. rayi, which constitutes the sole member of the monotypic family Bandringidae. The genus was described in 1969 by paleontologist Rainer Zangerl, and is known from exceptionally preserved individuals found in the Mazon Creek Lagerstätte of Illinois.

Squatinactis is a genus of extinct elasmobranch chondrichthyan known from the Carboniferous aged Bear Gulch Limestone in Montana. This fish was discovered in 1974 by Richard Lund. The type specimen, named CMNH 46133, consists of a brain case, poorly preserved jaws and gills, a pectoral fin, and a partial vertebral axis. This creature's most startling feature were its broad pectoral fins which resembled those of stingrays and angel sharks (Squatina). The holotype specimen has about 15 teeth in its jaw. This creature is named after the angel shark. Remains found in the South Urals of Russia and