| Characiformes | |
|---|---|
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| Hyphessobrycon bentosi | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| (unranked): | Otophysi |
| Order: | Characiformes Regan, 1911 |
| Type species | |
| Charax gibbosus | |
| Suborders, Infraorders, Superfamilies, and Families | |
Characiformes/ˈkærəsɪfɔːrmiːz/ is an order ofray-finned fish, comprising the characins and their allies. Grouped in 18 recognized families, more than 2000 different species are described, including the well-knownpiranha andtetras.[1]
The Characiformes form part of a series called theOtophysi within the superorderOstariophysi. The Otophysi contain three other orders,Cypriniformes,Siluriformes, andGymnotiformes.[1] The Characiformes form a group known as the Characiphysi with the Siluriformes and Gymnotiformes.[2] The order Characiformes is thesister group to the orders Siluriformes and Gymnotiformes, though this has been debated in light of recent molecular evidence.[1]
Originally, the characins were all grouped within a single family, theCharacidae. Since then, 18 different families have been separated out. However, classification varies somewhat, and the most recent (2011) study confirms the circumscribed Characidae asmonophyletic.[3] Currently, 18families, about 270genera, and at least 1674species are known.[3]
The suborderCitharinoidei, which contains the familiesDistichodontidae andCitharinidae, is considered the sister group to the rest of the characins, suborderCharacoidei.[2] This group has a very ancient divergence from the rest of the Characiformes, dating back to theEarly Cretaceous or earlier, and it has been suggested that it be better treated as its own order, theCithariniformes.[4]
The Characiformes likely first originated and diversified on the supercontinent ofWest Gondwana (composed of modern Africa and South America) during the Cretaceous period, though fossils are poorly known.[1] During the Cretaceous Period, the rift between South America and Africa would be forming; this may explain the contrast in diversity between the two continents. Their low diversity in Africa may explain why some primitive fish families and the Cypriniformes coexist with them whereas they are absent in South America, where these fish may have been driven extinct.[2] The characiforms had not spread into Africa soon enough to also reach the land connection between Africa and Asia.[2] The earliest they could have spread into Central America was the lateMiocene.[2]
The earliest characiform fossils date back to the Late Cretaceous, around theSantonian.[5] Other fossil teeth date back to theCenomanian ofMorocco, but it has been suggested that these teeth may be of earlyginglymodians.[4] Previously, the oldest characiform was assumed to beSantanichthys of the EarlyCretaceous (Albian Age) ofBrazil. This presumably marine taxon was used as evidence of characiformes potentially having marine origins.[6] However, more recent studies indicate thatSantanaichthys is likely a basalotophysan rather than a characiform. Similarly,Salminops from Spain andSorbinicharax from Italy, previously also considered potential marine characiforms, are now thought to have no characiform affinities and are considered indeterminateteleosts. Given this, there is no paleontological support for characiforms having marine origins.[7][8]
Uniquely, Late Cretaceous characiform fossils are found significantly north of their modern distribution. Indeterminate characiform teeth are known from the Santonian of Hungary andMaastrichtian of France, which have a large, multi-cusped appearance reminiscent of Africanalestids.[9] Similarly, twoCampanian freshwater characiform genera,Primuluchara andEotexachara, are known from North America, withPrimuluchara having a very wide distribution acrossLaramidia, ranging from Texas to as far north as southern Canada (Dinosaur Park Formation). It is likely that the warmer conditions of the Late Cretaceous allowed early characins to range farther north than the present day, with African characins colonizing Europe and South American characins colonizing North America. Early characins may have had some level of salt tolerance, allowing for such colonizations to take place.[10]
Within their modern distribution, a number of modern South American characin families have their earliest occurrences in the Maastrichtian of Bolivia, with isolated teeth and skeletal elements identifiable toAcestrorhynchidae,Characidae, andSerrasalmidae.[4]
Below is a phylogeny of living Characiformes based on Betancur-Rodriguezet al. 2017[11] and Nelson, Grande & Wilson 2016.[12]
| Characiformes |
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Characins possess aWeberian apparatus, a series ofbony parts connecting theswim bladder andinner ear.[1] Superficially, the Characiformes somewhat resemble their relatives of the orderCypriniformes, but have a small, fleshyadipose fin between thedorsal fin andtail. Most species have teeth within the mouth, since they are oftencarnivorous. The body is almost always covered in well-defined scales. The mouth is also usually not truly protractile.[13]
The largest characins areHydrocynus goliath andSalminus franciscanus andHoplias aimara,[14] both of which are up to 1.2 m (3.9 ft). The smallest in size is about 1.7 cm (0.67 in) in the Bolivian pygmy blue characin,Xenurobrycon polyancistrus.[15] Many members are under 3 cm (1.2 in).[1]
Characins are most diverse in theNeotropics, where they are found in lakes and rivers throughout most ofSouth andCentral America. Thered-bellied piranha, a member of the familySerrasalmidae within the Characiformes, is endemic to the Neotropical realm. At least 209 species of characins are found in Africa, including thedistichodontids,citharinids,alestids, andhepsetids. The rest of the characins originate from theAmericas.[1]
A few characins become quite large, and are important as food or game.[1] Most, however, are small shoaling fish. Many species commonly calledtetras are popular in aquaria[16] because of their bright colors, general hardiness, and tolerance towards other fish in community tanks.[1]
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{{cite book}}: CS1 maint: multiple names: authors list (link); Buckup P.A.: "Relationships of the Characidiinae and phylogeny of characiform fishes (Teleostei: Ostariophysi)",Phylogeny and Classification of Neotropical Fishes, L.R. Malabarba, R.E. Reis, R.P. Vari, Z.M. Lucena, eds. (Porto Alegre: Edipucr) 1998:123-144.