Saurichthys
Saurichthys (from , 'lizard' and 'fish') is an extinct genus of predatory ray-finned fish from the Triassic period. It is the name giving genus of the family Saurichthyidae (Changhsingian-Middle Jurassic). This family also includes the Permian "Eosaurichthys" (China) and the Jurassic "Saurorhynchus" (= "Acidorhynchus") from Europe and North America. Fossils of "Saurichthys" have been found on all continents except South America and Antarctica. It inhabited both marine and freshwater environments. The oldest fossils of "Saurichthys" were recovered from the Wordie Creek Formation in East Greenland and are Griesbachian (Induan, Early Triassic) in age. Over 50 species of "Saurichthys  have been described (see list below). The species differ in size and show variability in their skeletal features. The latter can potentially be ascribed to changes in major developmental genes. The use of subgenera (Eosaurichthys", "Costasaurichthys", "Lepidosaurichthys", "Saurorhynchus", "Sinosaurichthys") in the literature reflects differences in morphology between species groups. Several species that were described predominantly in the 19th century are based on fragmentary fossils (often isolated teeth). These are mostly considered invalid species by modern taxonomic standards. Louis Agassiz, who described the type species of "Saurichthys" in 1834, named it the "lizard fish" because of skeletal features that he thought  were intermediate to reptiles and fishes. Their closest modern-day relatives include the sturgeons, paddlefish, and the bowfins. However, a recent study investigated the inner skull anatomy of "Saurichthys" and questioned a close affiliation with Acipenseriformes and Amiiformes. Appearance. "Saurichthys" was an elongate, streamlined fish, commonly about to long. Some species were only a few decimetres long (e.g. "Saurichthys minimahleri"), while others could grow up to about in length (specimen from the Middle Triassic of Turkey). Species of "Saurichthys" looked superficially similar to the modern pike (note that the pike is a teleost and only distantly related with "Saurichthys"). Its  dorsal and anal fins were placed opposite each other well back on the body, and the tail was symmetrical. These features would have made it a powerful swimmer, and it is presumed to have hunted in a similar way to the pike, attacking from an ambush at high speed. Its jaws were extremely long, making up a third of the total body length, and ended in a sharp, beak-like tip. Two to six longitudinal scale rows are developed, with small scales in between in some species. The caudal fin is abbreviate-diphycercal. The axial skeleton consists of ossified neural  and haemal arches. Haemal arches may develop spines. The neural arches often show spines as well as other projections interpreted as prezygapophyses and postzygapophyses. Ossified centra are missing. The axial skeleton shows regionalization, meaning that there are differences in bone morphology between segments of the axial skeleton. Some species show dedifferentiation of the axial skeleton. Early Triassic species of "Saurichthys" differ from later species most prominently in their more elongate postorbital portion of the skull (part of the skull behind the eyes) and their generally denser scale cover. Ecology. Large species of "Saurichthys" were apex predators among Triassic ray-finned  fish, together with the marine "Birgeria" (Birgeriidae). "Saurichthys" is classically interpreted as an ambush predator. It first approached its prey and then attacked it by quick, sudden darts. Some species may have lived as subsurface cruisers ("Sinosaurichthys"). Specimens showing half-swallowed conspecific individuals suggest that cannibalism was relatively common in "Saurichthys". Fossil evidence, in the form of a bolus (ball-shaped mass) of bones in the same strata, indicates that "Saurichthys" attacked marine reptiles such as the tanystropheid "Langobardisaurus", or possibly scavenged their corpses. A study on the gastrointestinal tract of "Saurichthys" found similarities with present-day sharks and rays , in particular the many windings in the spiral valve. The many windings increased the surface area for digestion, which is sure to have provided the fish with more energy. It indicates that "Saurichthys" had an energy-laden lifestyle. Reproduction. Fossils of gravid females provide evidence for (ovo-)viviparity in "Saurichthys" and the oldest known example for viviparity in ray-finned fishes. Internal fertilisation is also evidenced by specialized pelvic fin rays ("Saurichthys calcaratus") or ventral scales (gonopodium; "Saurichthys curionii", "Saurichthys macrocephalus") that are interpreted as copulatory organs of males.