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Characiformes

Article Discussion

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Characiformes Template:IPAc-en is an order of ray-finned fish, comprising the characins and their allies. Grouped in 18 recognized families, more than 2000 different species are described, including the well-known piranha and tetras.<ref name=nelson>Template:Cite book; 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.</ref>

TaxonomyEdit

The Characiformes form part of a series called the Otophysi within the superorder Ostariophysi. The Otophysi contain three other orders, Cypriniformes, Siluriformes, and Gymnotiformes.<ref name=nelson/> The Characiformes form a group known as the Characiphysi with the Siluriformes and Gymnotiformes.<ref name=briggs/> The order Characiformes is the sister group to the orders Siluriformes and Gymnotiformes, though this has been debated in light of recent molecular evidence.<ref name=nelson/>

Originally, the characins were all grouped within a single family, the Characidae. Since then, 18 different families have been separated out. However, classification varies somewhat, and the most recent (2011) study confirms the circumscribed Characidae as monophyletic.<ref name=phylogenetic>Claudio Oliveira, Gleisy S Avelino, Kelly T Abe, Tatiane C Mariguela, Ricardo C Benine, Guillermo Ortí, Richard P Vari and Ricardo M Corrêa e Castro,"Phylogenetic relationships within the speciose family Characidae (Teleostei: Ostariophysi: Characiformes) based on multilocus analysis and extensive ingroup sampling", BMC Evolutionary Biology 2011, 11:275).</ref> Currently, 18 families, about 270 genera, and at least 1674 species are known.<ref name=phylogenetic/>

The suborder Citharinoidei, which contains the families Distichodontidae and Citharinidae, is considered the sister group to the rest of the characins, suborder Characoidei.<ref name="briggs">Template:Cite journal</ref> This group has a very ancient divergence from the rest of the Characiformes, dating back to the Early Cretaceous or earlier, and it has been suggested that it be better treated as its own order, the Cithariniformes.<ref name=":0">Template:Cite journal</ref>

EvolutionEdit

The Characiformes likely first originated and diversified on the supercontinent of West Gondwana (composed of modern Africa and South America) during the Cretaceous period, though fossils are poorly known.<ref name="nelson" /> 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.<ref name="briggs" /> The characiforms had not spread into Africa soon enough to also reach the land connection between Africa and Asia.<ref name="briggs" /> The earliest they could have spread into Central America was the late Miocene.<ref name="briggs" />

FossilsEdit

File:Lignobrycon ligniticus (P9012).tif
Lignobrycon ligniticus, a fossil characiform from the Oligocene of Brazil

The earliest characiform fossils date back to the Late Cretaceous, around the Santonian.<ref>Template:Cite journal</ref> Other fossil teeth date back to the Cenomanian of Morocco, but it has been suggested that these teeth may be of early ginglymodians.<ref name=":0" /> Previously, the oldest characiform was assumed to be Santanichthys of the Early Cretaceous (Albian Age) of Brazil. This presumably marine taxon was used as evidence of characiformes potentially having marine origins.<ref name="Filleul2004">Template:Cite journal</ref> However, more recent studies indicate that Santanaichthys is likely a basal otophysan rather than a characiform. Similarly, Salminops from Spain and Sorbinicharax from Italy, previously also considered potential marine characiforms, are now thought to have no characiform affinities and are considered indeterminate teleosts. Given this, there is no paleontological support for characiforms having marine origins.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Uniquely, Late Cretaceous characiform fossils are found significantly north of their modern distribution. Indeterminate characiform teeth are known from the Santonian of Hungary and Maastrichtian of France, which have a large, multi-cusped appearance reminiscent of African alestids.<ref>Template:Cite journal</ref> Similarly, two Campanian freshwater characiform genera, Primuluchara and Eotexachara, are known from North America, with Primuluchara having a very wide distribution across Laramidia, 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.<ref>Template:Cite journal</ref> 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 to Acestrorhynchidae, Characidae, and Serrasalmidae.<ref name=":0" />

Characins appear to have inhabited Europe into the Paleogene, with fossil teeth reminiscent of Alestes known from the Early Eocene of Spain.<ref>Template:Cite journal</ref> Eurocharax Gaudant, 1980 is known from a fully-articulated specimen from the Oligocene of France, and appears to represent an estuarine taxon, although its phylogenetic position needs revision.<ref>Template:Cite journal</ref><ref name=":1">Template:Citation</ref> Two other alleged Eocene European characids, Prohydrocyon Piton, 1938 and Procharacinus Piton, 1938 from France, lack a Weberian apparatus and are very likely not characins, and instead may be related to the enigmatic Thaumaturus.<ref name=":1" /><ref>Template:Cite journal</ref>

TaxonomyEdit

File:Citharinus congicus.jpg
Citharinus congicus is a member of the most basal characiform lineage
File:Hydrocynus goliath Gifu.jpg
Hydrocynus goliath, from Africa, is one of the largest species in the order
File:Characiformes in the Munim River Basin.jpg
Diversity of characiforms from the Munim River basin
File:Peixes da planície de inundação do alto rio Paraná (3678425).png
Diversity of large-sized characiforms from the Paraná River basin

The following classification is based on Eschmeyer's Catalog of Fishes (2025),<ref name=":13">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> with suprafamilial divisions based on Betancur et al (2018) & Melo et al (2022):<ref name=":3">Template:Cite journal</ref><ref name=":2">Template:Cite journal</ref>

Fossil taxaEdit

PhylogenyEdit

Below is a phylogeny of living Characiformes based on Betancur-Rodriguez et al. 2017<ref>Template:Cite journal</ref> and Nelson, Grande & Wilson 2016.<ref>Template:Cite book</ref> Template:Clade

DescriptionEdit

Characins possess a Weberian apparatus, a series of bony parts connecting the swim bladder and inner ear.<ref name=nelson/> Superficially, the Characiformes somewhat resemble their relatives of the order Cypriniformes, but have a small, fleshy adipose fin between the dorsal fin and tail. Most species have teeth within the mouth, since they are often carnivorous. The body is almost always covered in well-defined scales. The mouth is also usually not truly protractile.<ref name=fishbase>{{#invoke:Cite taxon|main|fishbase|genus=|species=|subspecies=}}</ref>

The largest characins are Hydrocynus goliath and Salminus franciscanus and Hoplias aimara,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> both of which are up to Template:Convert. The smallest in size is about Template:Convert in the Bolivian pygmy blue characin, Xenurobrycon polyancistrus.<ref name=EoF>Template:Cite book</ref> Many members are under Template:Convert.<ref name=nelson/>

Distribution and habitatEdit

Characins are most diverse in the Neotropics, where they are found in lakes and rivers throughout most of South and Central America. The red-bellied piranha, a member of the family Serrasalmidae within the Characiformes, is endemic to the Neotropical realm. At least 209 species of characins are found in Africa, including the distichodontids, citharinids, alestids, and hepsetids. The rest of the characins originate from the Americas.<ref name=nelson/>

Relationship to humansEdit

A few characins become quite large, and are important as food or game.<ref name=nelson/> Most, however, are small shoaling fish. Many species commonly called tetras are popular in aquaria<ref>Template:Cite journal</ref> because of their bright colors, general hardiness, and tolerance towards other fish in community tanks.<ref name=nelson/>

ReferencesEdit

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