|Individual organisms from each major Euteleostomi group. Clockwise, starting from top left:|
Euteleostomi is a successful clade that includes more than 90% of the living species of vertebrates. Euteleostomes are also known as "bony vertebrates". Both its major subgroups are successful today: Actinopterygii includes most extant fish species, and Sarcopterygii includes the tetrapods.
"Osteichthyes" in the sense of "bony vertebrates" is synonymous with Euteleostomi, even though in Linnaean taxonomy the name (literally meaning "bony fish") traditionally referred to the paraphyletic group with the exclusion of tetrapods. The name Euteleostomi was coined as a monophyletic alternative that unambiguously includes the living tetrapods and is widely used in bioinformatics.
Euteleostomes originally all had endochondral bone, fins with lepidotrichs (fin rays), jaws lined by maxillary, premaxillary, and dentary bones composed of dermal bone, and lungs. Many of these characters have since been lost by descendant groups, however, such as lepidotrichs lost in tetrapods, and bone lost among the chondrostean fishes. Lungs have been retained in dipnoi (lungfish), and many tetrapods (birds, mammals, reptiles, and some amphibians). In many ray-finned fishes lungs have evolved into swim bladders for regulating buoyancy, while in others they continue to be used as respiratory gas bladders.
Euteleostomi contains the following subgroups:
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