Actinopterygii, members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of skin supported by radially extended thin bony spines called lepidotrichia, as opposed to the bulkier, fleshy lobed fins of the sister class Sarcopterygii. Resembling folding fans, the actinopterygian fins can easily change shape and wetted area, providing superior thrust-to-weight ratios per movement compared to sarcopterygian and chondrichthyian fins. The fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the articulation between these fins and the internal skeleton.
The bowfin is a bony fish, native to North America. Common names include mudfish, mud pike, dogfish, grindle, grinnel, swamp trout, and choupique. It is regarded as a relict, being one of only two surviving species of the Halecomorphi, a group of fish that first appeared during the Early Triassic, around 250 million years ago. The bowfin is often considered a "primitive fish" because they have retained some morphological characteristics of their early ancestors. It is one of two species in the genus Amia, along with Amia ocellicauda, the eyespot bowfin. The closest living relatives of bowfins are gars, with the two groups being united in the clade Holostei.
The Amiiformes order of fish has only two extant species, the bowfins: Amia calva and Amia ocellicauda, the latter recognized as a separate species in 2022. These Amiiformes are found in the freshwater systems of North America, in the United States and parts of southern Canada. They live in freshwater streams, rivers, and swamps. The order first appeared in the Triassic, and the extinct members include both marine and freshwater species, many of which are morphologically disparate from bowfins, such as the caturids.
Neopterygii is a subclass of ray-finned fish (Actinopterygii). Neopterygii includes the Holostei and the Teleostei, of which the latter comprise the vast majority of extant fishes, and over half of all living vertebrate species. While living holosteans include only freshwater taxa, teleosts are diverse in both freshwater and marine environments. Many new species of teleosts are scientifically described each year.
Lepisosteiformes is an order of ray-finned fish and the only living members of the clade Ginglymodi. Its only extant representatives are the gar, and it is defined as all members of Ginglymodi that are more closely related to gar than to the extinct Semionotiformes, the other major grouping of ginglymodians. They are one of two extant orders in the infraclass Holostei alongside the Amiiformes.
Holostei is a group of ray-finned bony fish. It is divided into two major clades, the Halecomorphi, represented by the single living genus, Amia with two species, the bowfins, as well as the Ginglymodi, the sole living representatives being the gars (Lepisosteidae), represented by seven living species in two genera. The earliest members of the clade, which are putative "semionotiforms" such as Acentrophorus and Archaeolepidotus, are known from the Middle to Late Permian and are among the earliest known neopterygians.
Calamopleurus is an prehistoric genus of marine holostean ray-finned fish from the Early Cretaceous of South America and northern Africa. It was a relative of the modern bowfin, with both belonging to the family Amiidae.
Watsonulus is an extinct genus of prehistoric ray-finned fish that lived during the Early Triassic epoch in what is now Madagascar. It may have also existed in what is now Himachal Pradesh, India, during the Induan age. The type species, described by Jean Piveteau, is Watsonia eugnathoides. Because "Watsonia" was preoccupied, the new genus name Watsonulus was later erected. The genus is named after David Meredith Seares Watson.
Halecostomi is the name of a group of neopterygian fish uniting the halecomorphs and the teleosts, the largest group of extant ray-finned fish.
Asialepidotus is an extinct genus of prehistoric marine ray-finned fish that lived during the Ladinian stage of the Middle Triassic epoch. It contains a single species, A. shingyiensis, from Guizhou, China.
Ainia is an extinct genus of prehistoric ray-finned fish that lived during the Kimmeridgian stage of the Late Jurassic epoch. It contains a single species, A. armata, known from the famous Solnhofen Limestone of Germany. It is a distant relative of the bowfin, although it is more closely related to genera such as Caturus and Osteorachis.
Allolepidotus is an extinct genus of prehistoric marine neopterygian ray-finned fish from the Middle Triassic epoch of what is now Italy, Spain, and Switzerland. It was formerly referred to the halecomorph order Panxianichthyiformes, but is now thought to be a member of the Ionoscopiformes.
Cipactlichthys is a genus of extinct marine holostean fish from the Lower Cretaceous of Mexico, distantly related to modern bowfins. The only known species is Cipactlichthys scutatus.
Amia, commonly called bowfin, is a genus of ray-finned fish related to gars in the infraclass Holostei. They are regarded as taxonomic relicts, being the sole surviving species of the order Amiiformes and clade Halecomorphi, which dates from the Triassic to the Eocene, persisting to the present. There are two living species in Amia, Amia calva and Amia ocellicauda, and a number of extinct species which have been described from the fossil record.
Sinamiidae is an extinct family of ray-finned fish. They are halecomorph fishes endemic to Early Cretaceous freshwater environments in East and Southeast Asia.
Ginglymodi is a clade of ray-finned fish containing modern-day gars (Lepisosteidae) & their extinct relatives in the order Lepisosteiformes, the extinct orders Semionotiformes and Kyphosichthyiformes, and various other extinct taxa. Ginglymodi is one of the two major subgroups of the infraclass Holostei, the other one being Halecomorphi, which contains the bowfin and eyespot bowfin and their fossil relatives.
Dapediidae is an extinct family of neopterygian ray-finned fish that lived from the Middle Triassic to Late Jurassic. It is the only family of the order Dapediiformes. Its members were historically placed within the ginglymodian family Semionotidae, but were moved to their own family in 1966.
Parasemionotiformes is an extinct order of neopterygian ray-finned fish that existed globally during the Triassic period. It comprises the families Parasemionotidae and Promecosominidae. Many of the included genera are monotypic and most species lived during the Early Triassic epoch.
Redfieldiiformes is an extinct order of ray-finned fish (actinopterygians) which lived from the Middle Triassic to Early Jurassic. Redfieldiiforms were fairly typical Triassic fish in overall anatomy. They had a fusiform body shape with thick, ganoine-covered scales. The dorsal and anal fins were large, positioned opposite from each other, and shifted back, close to the tail. The caudal fin was hemiheterocercal, with the vertebral column and body scales extending into an upper lobe equal in size and shape to the lower lobe. They also had several characteristic skeletal traits, such as a hatchet-shaped preopercle, a series of fulcra fringing the fins, a reduced number of branchiostegal rays, and a snout ornamented with tubercles.
Fishes are a paraphyletic group and for this reason, the class Pisces seen in older reference works is no longer used in formal taxonomy. Traditional classification divides fish into three extant classes, and with extinct forms sometimes classified within those groups, sometimes as their own classes:
