Acipenseriformes is an

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

ray-finned fishes that includes living and fossil

sturgeon Sturgeon is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretace ...

s and paddlefishes (Acipenseroidei), as well as the

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

families Chondrosteidae and

Peipiaosteidae Peipiaosteidae is an extinct family of fish, known from the Late Jurassic and Early Cretaceous of Asia. They are members of Acipenseriformes, related to sturgeons (Acipenseridae) and paddlefish (Polyodontidae). Fossils have been found in freshwate ...

. They are the second earliest diverging group of living ray-finned fish after the bichirs. Despite being early diverging, they are highly

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

, having only weakly ossified skeletons that are mostly made of

cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck an ...

, and in modern representatives highly modified skulls.

Description

The axial skeleton of Acipenseriformes is only partially ossified, with the majority of the bones being replaced with cartilage. The

notochord In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consis ...

, usually only found in fish embryos, is unconstricted and retained throughout life. The premaxilla and maxilla bones of the skull present in other vertebrates have been lost. The

infraorbital nerve The infraorbital nerve is a branch of the maxillary nerve, itself a branch of the trigeminal nerve (CN V). It travels through the orbit and enters the infraorbital canal to exit onto the face through the infraorbital foramen. It provides sensory ...

is carried by a series of separate canals, rather than being within the circumorbital bones. The palatoquadrate bones of the skull possess a cartilaginous symphysis (joint), and also have a broad autopalatine plate, as well as a narrow palatoquadrate bridge, and a quadrate flange. The quadratojugal bone is three-pointed (triradiate), and the dentition on the gill-arch is confined to the upper part of the first arch and to only the first and second hypobranchials. Members of Acipenseriformes retain the ability to sense electric fields ( electroreception) using structures called

ampullae An ampulla (; ) was, in Ancient Rome, a small round vessel, usually made of glass and with two handles, used for sacred purposes. The word is used of these in archaeology, and of later flasks, often handle-less and much flatter, for holy water or ...

. This ability was present in the last common ancestor of all living jawed fish, but was lost in the ancestor of

neopterygian Neopterygii (from Greek νέος ''neos'' 'new' and πτέρυξ ''pteryx'' 'fin') 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 f ...

fish. All Acipenseriformes probably possessed barbels like modern sturgeon (which have four) and paddlefish (which have two).

Evolutionary history

Acipenseriformes are assumed to have evolved from a "

palaeonisciform The Palaeonisciformes (Palaeoniscida) are an extinct order of early ray-finned fishes ( Actinopterygii). Palaeonisciformes ''sensu lato'' first appeared in the fossil record in the Late Silurian and last appeared in the Late Cretaceous. The na ...

" ancestor. Their closest relatives within the paleonisciformes are uncertain and contested. ''

Eochondrosteus ''Eochondrosteus'' is a genus of extinct actinopterygian (ray-finned fish), comprising one species, ''E. sinensis'' (monotypy) from the Early Triassic strata in Gansu Province (Beishan Hills), China (previously interpreted as Permian in age). It ...

'' from the Early Triassic of China has been suggested by some authors to be the oldest acipenseriform. The oldest unambiguous members of the order are the Chondrosteidae, a group of large fish found in marine deposits from the Early Jurassic of Europe, which already have reduced ossification of the skeleton. The

are known from Middle Jurassic-Early Cretaceous freshwater deposits in Asia. The oldest known paddlefish is '' Protopsephurus'' from the Early Cretaceous of China, while the earliest known sturgeons appear in the Late Cretaceous in North America and Asia.

Classification

* Order Acipenseriformes Berg, 1940 ** Genus †''

''? Lu, Li & Yang, 2005 ** Family † Chondrosteidae

Egerton Egerton may refer to: People * Egerton (name), a list of people with either the surname or the given name * Egerton family, a British aristocratic family * George Egerton, pen name of Mary Dunne Bright (1859–1945), Australian-born writer Place ...

, 1858 *** Genus †'' Chondrosteus''

Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he rec ...

, 1833–1844 *** Genus †'' Gyrosteus'' Agassiz, 1833–1844 *** Genus †'' Strongylosteus'' Agassiz, 1833–1844 ** Family †

Liu & Zhou, 1965 *** Genus †'' Spherosteus'' Jakovlev, 1968 *** Genus †'' Yanosteus'' Jin et al., 1995 *** Genus †'' Liaosteus'' Lu, 1995 *** Genus †'' Peipiaosteus'' Liu & Zhou, 1965 *** Genus †'' Stichopterus'' Reis, 1909 **Suborder Acipenseroidei Grande & Bemis, 1991 *** Family

Polyodontidae Paddlefish (family Polyodontidae) are a family of ray-finned fish belonging to order Acipenseriformes, and one of two living groups of the order alongside sturgeons (Acipenseridae). They are distinguished from other fish by their titular elongla ...

Bonaparte, 1838 (Paddlefish) **** Genus †'' Protopsephurus'' Lu, 1994 **** Genus †'' Paleopsephurus'' MacAlpin, 1941a **** Subfamily Polyodontinae Grande & Bemis, 1991 non Pflugfelder, 1934 ***** Genus †'' Crossopholis'' Cope, 1883 ***** Genus '' Polyodon''

Lacépède Lacepede can refer to: * Bernard Germain de Lacépède (1756–1825), French naturalist and politician. * Lacepede Bay, a bay in South Australia. * Lacépède, Lot-et-Garonne, a ''commune'' in France * Lacepede Islands, a group of four islands in t ...

, 1797 (American paddlefish) ***** Genus †''

Psephurus The Chinese paddlefish (''Psephurus gladius''; : literal translation: "white sturgeon"), also known as the Chinese swordfish, is an extinct species of fish that was formerly native to the Yangtze and Yellow River basins in China. With records ...

'' Günther, 1873 (Chinese paddlefish) *** Family

Acipenseridae Sturgeon is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the Late Cretaceous, and are descended from other, earlier acipenseriform fish, which date back to the Early ...

Bonaparte, 1831 sensu Bemis et al., 1997 (Sturgeons) **** Genus †'' Protoscaphirhynchus'' Wilimovsky, 1956 **** Genus † '' Engdahlichthys'' Murray et al. 2020 **** Genus †'' Anchiacipenser'' Sato, Murray, Vernygora and Currie, 2019 **** Genus †'' Priscosturion'' Grande & Hilton, 2009 'Psammorhynchus'' Grande & Hilton, 2006**** Genus '' Acipenser'' Linnaeus, 1758 **** Genus '' Huso'' J. F. Brandt & Ratzeburg, 1833 **** Genus '' Scaphirhynchus'' Heckel, 1835 **** Genus '' Pseudoscaphirhynchus'' Nikolskii, 1900

Conservation

Most living species of Acipenseriformes are classified as threatened (mostly endangered or critically endangered) by the International Union for Conservation of Nature. The Chinese paddlefish was last seen alive in 2003, and was considered to have gone extinct sometime between 2005 and 2010 by the Yangtze River Fisheries Research Institute in their 2019 report.

Hybridization

A study published in 2020 reported a successful

hybridization Hybridization (or hybridisation) may refer to: *Hybridization (biology), the process of combining different varieties of organisms to create a hybrid *Orbital hybridization, in chemistry, the mixing of atomic orbitals into new hybrid orbitals *Nu ...

between a Russian sturgeon (''Acipenser gueldenstaedtii'') and an

American paddlefish The American paddlefish (''Polyodon spathula,'' also known as a Mississippi paddlefish, spoon-billed cat, or spoonbill) is a species of ray-finned fish. It is the only living species of paddlefish (Polyodontidae). This family is most closely r ...

(''Polyodon spathula''), indicating that the two species can breed with one another despite their lineages having been separated for hundreds of millions of years. This has marked the first successful hybridization between members of

and

References

Martin Hochleithner Martin may refer to: Places * Martin City (disambiguation) * Martin County (disambiguation) * Martin Township (disambiguation) Antarctica * Martin Peninsula, Marie Byrd Land * Port Martin, Adelie Land * Point Martin, South Orkney Islands Aus ...

and Joern Gessner, ''The Sturgeons and Paddlefishes of the World: Biology and Aquaculture'' *

, Joern Gessner, and

Sergej Podushka Sergius is a male given name of Ancient Roman origin after the name of the Latin ''gens'' Sergia or Sergii of regal and republican ages. It is a common Christian name, in honor of Saint Sergius, or in Russia, of Saint Sergius of Radonezh, and ...

, ''The Bibliography of Acipenseriformes'' *

External links

Photos and illustrations of AcipenseriformesCITES finalizes 2006 caviar export quotas
{{Taxonbar, from=Q192422 Ray-finned fish orders Taxa named by Lev Berg Articles which contain graphical timelines Extant Late Jurassic first appearances