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 ''
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 ...
'' 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
See also
*
Acanthodii
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, whi ...
*
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 ...
References
{{Taxonbar, from=Q134681
Vertebrate unranked clades
Late Ordovician first appearances
Extant Ordovician first appearances
Taxa named by Charles Lucien Bonaparte