Osteichthyes

Osteichthyes ( /ˌɒstiːˈɪkθi.iːz/), also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species. It is the largest class of vertebrates in existence today. Osteichthyes is divided into the ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). The oldest known fossils of bony fish are about 420 million years ago, which are also transitional fossils, showing a tooth pattern that is in between the tooth rows of sharks and bony fishes.

In most classification systems the Osteichthyes are paraphyletic with land vertebrates. That means that the nearest common ancestor of all Osteichthyes includes tetrapods amongst its descendants. Actinopterygii (ray-finned fish) are monophyletic, but the inclusion of Sarcopterygii in Osteichthyes causes Osteichthyes to be paraphyletic. Paradoxically, Sarcopterygii is considered monophyletic, as it includes tetrapods.

Most bony fish belong to the ray-finned fish (Actinopterygii); there are only eight living species of non-tetrapod lobe-finned fish (Sarcopterygii), including the lungfish and coelacanths.

Traditionally, the bony fish had been treated as a class within the vertebrates, with Actinopterygii and Sarcopterygii as subclasses. However, some recent works have elevated Osteichthyes to superclass, with Actinopterygii and Sarcopterygii as classes.