Teleostomi is an obsolete clade of jawed vertebrates that supposedly includes the

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

s, bony fish, and the wholly extinct

acanthodian Acanthodii or acanthodians is an extinct class of gnathostomes (jawed fishes), typically considered a paraphyletic group. They are currently considered to represent a grade of various fish lineages leading up to the extant Chondrichthyes, which ...

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 Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue. C ...

and the extinct class

Placodermi Placodermi (from Greek πλάξ 'plate' and δέρμα 'skin', literally ' plate-skinned') is a class of armoured prehistoric fish, known from fossils, which lived from the Silurian to the end of the Devonian period. Their head and thorax were co ...

. Recent studies indicate that Osteichthyes evolved from

placoderms Placodermi (from Greek πλάξ 'plate' and δέρμα 'skin', literally 'plate-skinned') is a class of armoured prehistoric fish, known from fossils, which lived from the Silurian to the end of the Devonian period. Their head and thorax were ...

like ''

Entelognathus ''Entelognathus primordialis'' (“primordial complete jaw”) is a maxillate placoderm from the late Silurian (Ludlow epoch) of Qujing, Yunnan, 419 million years ago. A team led by Min Zhu of the Academy of Sciences' Institute of Vertebrate Pa ...

'', while acanthodians are more closely related to modern chondrichthyes. Teleostomi, therefore, is not a valid, natural clade, but a

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

group of species. The clade Teleostomi should not be confused with the similar-sounding fish clade

Teleostei Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Te ...

Origins

The origins of the teleostomes are obscure. They are traditionally assumed to be descendants of the

Acanthodian Acanthodii or acanthodians is an extinct class of gnathostomes (jawed fishes), typically considered a paraphyletic group. They are currently considered to represent a grade of various fish lineages leading up to the extant Chondrichthyes, which ...

s ("spiny sharks") from the Early Silurian Period; however, more recent discoveries show that the "spiny sharks" are actually a paraphyletic assemblage leading to

Chondrichthyes Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue. ...

, and that placoderms like ''

'' are more closely related to true bony fish. Living teleostomes constitute the clade

Euteleostomi Euteleostomi (''Eu-teleostomi'', where ''Eu-'' comes from Greek εὖ 'well, good' or Euteleostomes, also known as "bony vertebrates") is a successful clade that includes more than 90% of the living species of vertebrates. Both its major subgro ...

, which includes all osteichthyans and tetrapods. Even after the acanthodians perished at the end of the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...

, 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 Aquatic respiration is the process whereby an aquatic organism exchanges respiratory gases with water, obtaining oxygen from oxygen dissolved in water and excreting carbon dioxide and some other metabolic waste products into the water. Unicel ...

. First, the early teleostomes probably had some type of operculum; however, it was not the one-piece affair of living

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...

. 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 Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

. This developed, in later species, into the lung and (later) the swim bladder, used to keep the fish at neutral buoyancy. Acanthodians share with Actinopterygii the characteristic of three

otolith An otolith ( grc-gre, ὠτο-, ' ear + , ', a stone), also called statoconium or otoconium or statolith, is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in the vestibular system of vertebrates. The sa ...

s, 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

References

{{Taxonbar, from=Q134681 Vertebrate unranked clades Late Ordovician first appearances Extant Ordovician first appearances Taxa named by Charles Lucien Bonaparte

Origins

Physical characteristics

Relationships

See also

References