Acipenseriformes is an order of basal

ray-finned fishes Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...

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

paddlefish 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 ...

es (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 Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...

Chondrosteidae Chondrosteidae is a family (biology), family of extinct marine actinopterygian fishes in the order Acipenseriformes. Three genera are known from the Early Jurassic of Europe, ''Chondrosteus'', ''Gyrosteus'', and ''Strongylosteus''. Included sp ...

and Peipiaosteidae. They are the second earliest diverging group of living ray-finned fish after the

bichir Bichirs and the reedfish comprise Polypteridae , a family of archaic ray-finned fishes and the only family in the order Polypteriformes .Helfman GS, Collette BB, Facey DE, Bowen BW. 2009. The Diversity of Fishes. West Sussex, UK: Blackwell Pu ...

s. 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 Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by Cell (biology), cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes ...

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

, 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 The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

and

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

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 In some fishes, the palatoquadrate is the dorsal component of the mandibular arch, the ventral one being Meckel's cartilage. The palatoquadrate forms from splanchnocranium in various chordates including placoderms and acanthodians. See also * ...

bones of the skull possess a cartilaginous

symphysis A symphysis (, pl. symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing togethe ...

(joint), and also have a broad autopalatine plate, as well as a narrow palatoquadrate bridge, and a quadrate flange. The

quadratojugal bone The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...

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 Electric Fields are an Aboriginal Australian electronic music duo made up of vocalist Zaachariaha Fielding and keyboard player and producer Michael Ross. Electric Fields combine modern electric-soul music with Aboriginal culture and sing in Pi ...

(

electroreception Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stu ...

) 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 In fish anatomy and turtle anatomy, a barbel is a slender, whiskerlike sensory organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, the hagfish, the sturgeon, the zebrafish, the black dragonfish and some s ...

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'' 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

, a group of large fish found in marine deposits from the Early Jurassic of Europe, which already have reduced ossification of the skeleton. The Peipiaosteidae are known from Middle Jurassic-Early Cretaceous freshwater deposits in Asia. The oldest known paddlefish is ''

Protopsephurus ''Protopsephurus'' is an extinct genus of paddlefish containing the single species ''Protopsephurus liui,'' known from the Yixian Formation in Liaoning, northern China from the Barremian to Aptian ages of the Early Cretaceous period around 125-12 ...

'' 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 Berg may refer to: People *Berg (surname), a surname (including a list of people with the name) *Berg Ng (born 1960), Hong Kong actor * Berg (footballer) (born 1989), Brazilian footballer Former states * Berg (state), county and duchy of the Hol ...

, 1940 ** Genus †'' Eochondrosteus''? Lu, Li & Yang, 2005 ** Family †

Egerton, 1858 *** Genus †''

Chondrosteus ''Chondrosteus'' is a genus of extinct actinopterygian (ray-finned fish) belonging to the family Chondrosteidae. It lived during the Sinemurian (early Early Jurassic) in what is now England. ''Chondrosteus'' is remotely related to sturgeons and ...

'' Agassiz, 1833–1844 *** Genus †''

Gyrosteus ''Gyrosteus'' is an extinct genus of very large ray-finned fish belonging to the family Chondrosteidae. It comprises the type species, ''Gyrosteus mirabilis'', which lived during the early Toarcian (Late Early Jurassic) in what is now northern E ...

'' Agassiz, 1833–1844 *** Genus †''

Strongylosteus ''Strongylosteus'' is an extinct genus of prehistoric ray-finned fish that lived during the early Toarcian age of the Early Jurassic epoch.Hennig, E. (1925). ''Chondrosteus Hindenburgi'' Pomp.---Ein «Stör» des württembergischen Ölschiefers ...

'' Agassiz, 1833–1844 ** Family † Peipiaosteidae Liu & Zhou, 1965 *** Genus †'' Spherosteus'' Jakovlev, 1968 *** Genus †'' Yanosteus'' Jin et al., 1995 *** Genus †'' Liaosteus'' Lu, 1995 *** Genus †''

Peipiaosteus ''Peipiaosteus'' is an extinct genus of prehistoric chondrostean ray-finned fish. Its fossils are found in the Early Cretaceous Jiufotang Formation, Pani Lake, Liaoning Province, China.Liu, H. T. and Zhou, J . J. 1965A new sturgeon from the ...

'' Liu & Zhou, 1965 *** Genus †''

Stichopterus ''Stichopterus'' is an extinct genus of chondrostean ray-finned fish that lived during the Early Cretaceous epoch in Asia. It has been found in Russia (Murtoi Formation) and Mongolia. The type species, ''Stichopterus woodwardi'', was named an ...

'' 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 †''

'' Lu, 1994 **** Genus †''

Paleopsephurus ''Palaeopsephurus'' is an extinct genus of paddlefish in the Acipenseriformes family Polyodontidae. At present the genus contains the single species ''Palaeopsephurus wilsoni''. The genus is known primarily from the Late Cretaceous (Maastricht ...

'' MacAlpin, 1941a **** Subfamily Polyodontinae Grande & Bemis, 1991 non Pflugfelder, 1934 ***** Genus †''

Crossopholis ''Crossopholis'' is an extinct bony fish known from the early Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozo ...

Cope The cope (known in Latin as ''pluviale'' 'rain coat' or ''cappa'' 'cape') is a liturgical vestment, more precisely a long mantle or cloak, open in front and fastened at the breast with a band or clasp. It may be of any liturgical colours, litu ...

, 1883 ***** Genus ''

Polyodon 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 extant taxon, living species of paddlefish (Polyodontidae). This family is m ...

'' Lacépède, 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 Bonaparte, 1831 sensu Bemis et al., 1997 (Sturgeons) **** Genus †''

Protoscaphirhynchus ''Protoscaphirhynchus squamosus'' is an extinct sturgeon from the Late Cretaceous of North America. It is known from a single poorly preserved specimen found in the Maastrichtian aged Hell Creek Formation in Montana. Due to its poor preservation ...

'' Wilimovsky, 1956 **** Genus † '' Engdahlichthys'' Murray et al. 2020 **** Genus †'' Anchiacipenser'' Sato, Murray, Vernygora and Currie, 2019 **** Genus †''

Priscosturion ''Priscosturion'' is a genus of sturgeon from the Judith River Formation. It lived during the Campanian stage of the Late Cretaceous some 77.5 million years ago. Initially called ''Psammorhynchus'', its describers Lance Grande and Eric J. Hilton ...

'' Grande & Hilton, 2009 'Psammorhynchus'' Grande & Hilton, 2006**** Genus ''

Acipenser ''Acipenser'' is a genus of sturgeons. With 17 living species (others are only known from fossil remains), it is the largest genus in the order Acipenseriformes. The genus is paraphyletic, containing all sturgeons that do not belong to ''Huso' ...

Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...

, 1758 **** Genus ''

Huso ''Huso'' is a genus of large sturgeons from Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Ib ...

'' J. F. Brandt &

Ratzeburg Ratzeburg (; Low German: ''Ratzborg'') is a town in Schleswig-Holstein, Germany. It is surrounded by four lakes—the resulting isthmuses between the lakes form the access lanes to the town. Ratzeburg is the capital of the district Herzogtum La ...

, 1833 **** Genus ''

Scaphirhynchus ''Scaphirhynchus'' is a genus of sturgeons native to the United States of America. All species in this genus are considered to be threatened. The pallid sturgeon is Endangered and the Alabama sturgeon is Critically Endangered. Distribution Memb ...

'' Heckel, 1835 **** Genus ''

Pseudoscaphirhynchus ''Pseudoscaphirhynchus'' is a genus of relatively small, highly threatened sturgeons that are restricted to the Aral Sea system (although extirpated from the Aral Sea itself), including the Amu Darya and Syr Darya river basins, in Central Asia. ...

'' Nikolskii, 1900

Conservation

Most living

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of Acipenseriformes are classified as

threatened Threatened species are any species (including animals, plants and fungi) which are vulnerable to endangerment in the near future. Species that are threatened are sometimes characterised by the population dynamics measure of ''critical depensat ...

(mostly

endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inva ...

or critically endangered) by the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

. The

Chinese paddlefish 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 of ...

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 The Chinese Academy of Fishery Sciences (CAFS) (; Pinyin: Zhōngguó shuǐchǎn Kēxuéyánjiūyuàn) is a large fisheries research institute. It was founded in 1978 under the Ministry of Agriculture in the People's Republic of China. It is a lea ...

in their 2019 report.

Hybridization

A study published in 2020 reported a successful hybridization between a

Russian sturgeon The Russian sturgeon (''Acipenser gueldenstaedtii''), also known as the diamond sturgeon or Danube sturgeon, is a species of fish in the family Acipenseridae. It is found in Azerbaijan, Bulgaria, Georgia, Iran, Kazakhstan, Romania, Russia, Turkey ...

(''Acipenser gueldenstaedtii'') and an American paddlefish (''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 Acipenseridae and

References

* Martin Hochleithner and Joern Gessner, ''The Sturgeons and Paddlefishes of the World: Biology and Aquaculture'' * Martin Hochleithner, Joern Gessner, and Sergej Podushka, ''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