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Teleostomi
From Wikipedia, the free encyclopedia
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Teleostomi is a clade of jawed vertebrates that includes the tetrapods, bony fish, and the wholly extinct acanthodian fish. Key characters of this group include an operculum and a single pair of respiratory openings, features which were lost or modified in some later representatives. The teleostomes include all jawed vertebrates except the chondrichthyans and the placoderms.
The clade Teleostomi should not be confused with the similar-sounding fish clade Teleostei.
The origins of the teleostomes are obscure, but their first known fossils are Acanthodians ("spiny sharks") from the Late Ordovician Period. Living teleostomes constitute the clade Euteleostomi, which includes all osteichthyans and tetrapods. Even after the acanthodians perished at the end of the Permian, their euteleostome relatives flourished such that today they comprise 99% of living vertebrate species.
Teleostomes have two major adaptations that relate to respiration. First, the early teleostomes probably had some type of operculum, however, it was not the one-piece affair of living fish. The development of a single respiratory opening seems to have been an important step. The second adaptation, the teleostomes also developed a swim bladder and the ability to use some atmospheric oxygen, if primarily for buoyancy, very early on. The primary function of the bladder is keeping the fish at neutral buoyancy. Later these swim bladders will evolve and modify into lungs, as in tetrapods.
Acanthodians share with Actinopterygii the characterstic of three otoliths, the sagitta in the sacculus, the asteriscus in the lagena, and the lapillus in the utriculus. In dipnoans there are only two otoliths and in Latimeria there is only one.[1]
- ^ Nelson, Joseph, S. (2006). Fishes of the World. John Wiley & Sons, Inc.. ISBN 0471250317.
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