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Subclass of fishes

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. 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. 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. Another study suggests an even earlier split (360 myr ago, near the Devonian Carboniferous boundary).

Living neopterygians are subdivided into two main groups (infraclasses): teleosts and holosteans. Holosteans comprise two clades, the Ginglymodi and the Halecomorphi. All of these groups have a long and extensive fossil record. 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). 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. 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. 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.