Teleostomi
Encyclopedia
Teleostomi is a clade
of jawed vertebrates
that includes the tetrapod
s, 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 placodermi
.
The clade Teleostomi should not be confused with the similar-sounding fish clade Teleostei
.
├─(unranked) Gnathostomatomorpha
└─Infraphylum Gnathostomata
├─Class Placodermi
— extinct (armored gnathostomes)
└Microphylum Eugnathostomata
(true jawed vertebrates)
├─Class Chondrichthyes
(cartilaginous fish)
└─(unranked) Teleostomi (Acanthodii & Osteichthyes)
├─Class Acanthodii
— extinct ("spiny sharks")
└Superclass Osteichthyes
(bony fish)
├─Class Actinopterygii
(ray-finned fish)
└─Class Sarcopterygii
(lobe-finned fish)
└Superclass Tetrapoda
├─Class Amphibia (amphibians)
└(unranked) Amniota (amniotic egg)
├─Class Sauropsida
(reptiles or sauropsids)
│ └─Class Aves
(birds)
└─Class Synapsida
└─Class Mammal
ia (mammals)
Note: lines show evolutionary relationships.
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.
. 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 Actinopterygii the characteristic of three otolith
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.
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
of jawed vertebrates
Gnathostomata
Gnathostomata is the group of vertebrates with jaws. The term derives from Greek γνάθος "jaw" + στόμα "mouth". Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates...
that includes the tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
s, bony fish
Osteichthyes
Osteichthyes , also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species...
, and the wholly extinct acanthodian
Acanthodii
Acanthodii is a class of extinct fishes, sharing features with both bony fish and cartilaginous fish. In form they resembled sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteans...
fish. Key characters of this group include an operculum
Operculum (fish)
The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body....
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
Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...
and the placodermi
Placodermi
Placodermi is a class of armoured prehistoric fish, known from fossils, which lived from the late Silurian to the end of the Devonian Period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked, depending on the species. Placoderms were...
.
The clade Teleostomi should not be confused with the similar-sounding fish clade Teleostei
Teleostei
Teleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes. This diverse group, which arose in the Triassic period, includes 20,000 extant species in about 40 orders; most living fishes are members of this group...
.
Taxonomy and phylogeny
Subphylum Vertebrata├─(unranked) Gnathostomatomorpha
└─Infraphylum Gnathostomata
├─Class Placodermi
Placodermi
Placodermi is a class of armoured prehistoric fish, known from fossils, which lived from the late Silurian to the end of the Devonian Period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked, depending on the species. Placoderms were...
— extinct (armored gnathostomes)
└Microphylum Eugnathostomata
Eugnathostomata
-Taxonomy and phylogeny: Subphylum Vertebrata └─Infraphylum Gnathostomata ├─Class Placodermi — extinct └Microphylum Eugnathostomata...
(true jawed vertebrates)
├─Class Chondrichthyes
Chondrichthyes
Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...
(cartilaginous fish)
└─(unranked) Teleostomi (Acanthodii & Osteichthyes)
├─Class Acanthodii
Acanthodii
Acanthodii is a class of extinct fishes, sharing features with both bony fish and cartilaginous fish. In form they resembled sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteans...
— extinct ("spiny sharks")
└Superclass Osteichthyes
Osteichthyes
Osteichthyes , also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species...
(bony fish)
├─Class Actinopterygii
Actinopterygii
The Actinopterygii or ray-finned fishes constitute a class or sub-class of the bony fishes.The ray-finned fishes are so called because they possess lepidotrichia or "fin rays", their fins being webs of skin supported by bony or horny spines , as opposed to the fleshy, lobed fins that characterize...
(ray-finned fish)
└─Class Sarcopterygii
Sarcopterygii
The Sarcopterygii or lobe-finned fishes – sometimes considered synonymous with Crossopterygii constitute a clade of the bony fishes, though a strict classification would include the terrestrial vertebrates...
(lobe-finned fish)
└Superclass Tetrapoda
├─Class Amphibia (amphibians)
└(unranked) Amniota (amniotic egg)
├─Class Sauropsida
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
(reptiles or sauropsids)
│ └─Class Aves
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
(birds)
└─Class Synapsida
└─Class Mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ia (mammals)
Note: lines show evolutionary relationships.
Origins
The origins of the teleostomes are obscure, but their first known fossils are Acanthodians ("spiny sharks") from the Late OrdovicianOrdovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
Period. Living teleostomes constitute the clade Euteleostomi
Euteleostomi
Euteleostomi is a successful clade that includes more than 90% of the living species of vertebrates. Euteleostomes are also known as "bony vertebrates". Both major subgroups are successful today: Actinopterygii includes the majority of extant fish species, and Sarcopterygii includes the tetrapods...
, which includes all osteichthyans and tetrapods. Even after the acanthodians perished at the end of the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "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 respirationAquatic respiration
Aquatic respiration is the process whereby an aquatic animal obtains oxygen from water.-Fish:In most fish respiration takes place through gills. Lungfish, however, possess one or two lungs...
. First, the early teleostomes probably had some type of operculum
Operculum (fish)
The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body....
, however, it was not the one-piece affair of living fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate 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...
. 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
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. 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
Otolith
An otolith, , also called statoconium or otoconium is a structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth of vertebrates. The saccule and utricle, in turn, together make the otolith organs. They are sensitive to gravity and linear acceleration...
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.