[6] Their closest living relatives are the Characiformes (characins, tetras and their kin), the Gymnotiformes (electric eel and American knifefishes), and the Siluriformes (catfishes).

Other differences are the Cypriniformes' unique kinethmoid, a small median bone in the snout, and the lack of teeth in the mouth.

[8] Brackish water and marine cyprinids are invariably anadromous,[citation needed] swimming upstream into rivers to spawn.

[citation needed] A midsized group like the suckers,[11] they are rather similar to catfish in appearance and behaviour, feeding primarily off the substrate and equipped with barbels to help them locate food at night or in murky conditions.

While the Cyprinioidea seem more "primitive" than the loach-like forms,[5] they were apparently successful enough never to shift from the original ecological niche of the basal Ostariophysi.

While some details about the phylogenetic structures of this massively diverse family are known – e.g. that Cultrinae and Leuciscinae are rather close relatives and stand apart from Cyprininae – no good consensus exists yet on how the main lineages are interrelated.

A systematic list, from the most ancient to the most modern lineages, can thus be given as:[15] Phylogeny based on the work of the following works[17][18][19][20][21] Cyprinidae (carps & minnows) Psilorhynchidae Catostomidae Gyrinocheilidae Botiidae Vaillantellidae Cobitidae Balitoridae Ellopostomatidae Nemacheilidae Cypriniformes include the most primitive of the Ostariophysi in the narrow sense (i.e. excluding the Gonorynchiformes).

The earliest that Cypriniformes might have diverged from Characiphysi (Characiformes and relatives) is thought to be about the Early Triassic, about 250 million years ago (mya).

If this were the case, they would have spread to Asia through Africa or North America before the continents split up, for these are purely freshwater fishes.

[24] The earliest cypriniform fossils are already assignable to the living family Catostomidae; from the Paleocene of Alberta, they are roughly 60 million years old.

Habitat destruction, damming of upland rivers, pollution, and in some cases overfishing for food or the pet trade have driven some Cypriniformes to the brink of extinction or even beyond.

In particular, Cyprinidae of southwestern North America have been severely affected; a considerable number went entirely extinct after settlement by Europeans.

For example, in 1900 the thicktail chub (Gila crassicauda) was the most common freshwater fish found in California; 70 years later, not a single living individual existed.

Ironically, while pollution and other forms of overuse by humans have driven it from its native home, it is bred for the aquarium fish trade by the thousands.