Neopterygii

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 fishes, and over half of all living vertebrate species.^[3] While living holosteans include only freshwater taxa, teleosts are diverse in both freshwater and marine environments. Many new species of teleosts are scientifically described each year.^[3]

Fossil evidence for crown group neopterygians goes back at least 251 million years to the Induan stage of the Early Triassic epoch,^[4][5][6] however, one study incorporating morphological data from fossils and molecular data from nuclear and mitochondrial DNA, places this divergence date at least 284 mya (million years ago), during the Artinskian stage of the Early Permian.^[1] Another study suggests an even earlier split (360 myr ago, near the Devonian-Carboniferous boundary).^[7]

Vertebrates

Jawless fish (118 living species: hagfish, lampreys)

Jawed vertebrates

Cartilaginous fishes (>1,100 living species: sharks, rays, chimaeras)

Bony fishes Lobe-fins Rhipidistia

Tetrapoda (>30,000 living species: amphibians, mammals, reptiles, birds)

Dipnoi (6 living species: lungfish)

Actinistia (2 living species: coelacanths)

Ray-fins

Cladistia (14 living species: bichirs, reedfish)

Actinopteri

Chondrostei (27 living species: sturgeons, paddlefish)

Neopterygii (>32,000 living species)

Evolution and diversity

Living neopterygians are subdivided into two main groups (infraclasses): teleosts and holosteans.^[8] Holosteans comprise two clades, the Ginglymodi and the Halecomorphi.^{[9][3][10][11]} All of these groups have a long and extensive fossil record.^[12] The evolutionary relationships between the different groups of Neopterygii is summarized in the cladogram below (divergence time for each clade in mya are based on^[7]).

Neopterygii 360 mya Holostei 275 mya

Ginglymodi (7 living species: gars and alligator gars)

Halecomorphi (1 living species: bowfin)

310 mya

Teleostei (>32,000 living species)

Neopterygians are a very speciose group. They make up over 50% of the total vertebrate diversity today, and their diversity grew since the Mesozoic era.^[12][13] However, the diversity of the various groups of neopterygians (or of fishes in general) is unevenly distributed, with teleosts making up the vast majority (96%) of living species.^[3]

Early in their evolution, neopterygians were a very successful group of fish, because they could move more rapidly than their ancestors. Their scales and skeletons began to lighten during their evolution, and their jaws became more powerful and efficient.^[3] While electroreception and the ampullae of Lorenzini are present in all other groups of fish, with the exception of hagfish (although hagfish are not actinopterygians, they are agnathans), neopterygians have lost this sense, even if it has later been re-evolved within Gymnotiformes and catfishes, which possess non-homologous teleost ampullae.^[14]

Only a few changes occurred during the evolution of neopterygians from the earlier actinopterygians. However, a very important step in the evolution of neopterygians is the acquisition of a better control of the movements of both dorsal and anal fins, resulting in an improvement in their swimming capabilities. They additionally acquired several modifications in the skull, which allowed the evolution of different feeding mechanisms and consequently the colonization of new ecological niches. All of these characters represented major improvements, resulting in Neopterygii becoming the dominant group of fishes (and, thus, taxonomically of vertebrates in general) today.^[12]

The great diversity of extant teleosts has been linked to a whole genome duplication event during their evolution.^[15]

Classification

References

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