Teleostomi (from Greek language τελεος, complete + Greek στόμα, mouth) is an obsolete taxon
Recent studies indicate that Osteichthyes evolved from placoderms like Entelognathus, while acanthodians are more closely related to modern chondrichthyes. Teleostomi, therefore, is not a valid, natural clade, but a paraphyletic group of species.
Origins
The origins of the teleostomes are obscure. They are traditionally assumed to be descendants of the
("spiny sharks") from the
Llandovery epoch Period; however, more recent discoveries show that the "spiny sharks" are actually a paraphyletic assemblage leading to
Chondrichthyes, and that placoderms like
Entelognathus are more closely related to true bony fish.
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.
Physical characteristics
Teleostomes have two major adaptations that relate to aquatic 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 primitive lung with the ability to use some atmospheric
oxygen. This developed, in later species, into the lung and (later) the swim bladder, used to keep the fish at neutral buoyancy.
Acanthodians share with actinopterygians the characteristic of three , 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.
However, most of the above synapomorphies can ultimately be found in several chondrichthyan groups.
Relationships
