Teleostomi (from

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

τελεος, complete + Greek στόμα, mouth) is an obsolete taxon of jawed vertebrates that supposedly includes the

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

, and the wholly extinct

acanthodian Acanthodii or acanthodians is an extinct class of Gnathostomata, gnathostomes (jawed fishes). They are currently considered to represent a paraphyletic Evolutionary grade, grade of various fish lineages Basal (phylogenetics), basal to extant tax ...

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

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

Placodermi Placoderms (from Ancient Greek πλάξ 'plax'', ''plakos plate' and δέρμα 'dermaskin') are vertebrate animals of the class Placodermi, an extinct group of prehistoric fish known from Paleozoic fossils during the Silurian and the De ...

. Recent studies indicate that

Osteichthyes Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

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 Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

group of species.

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 Gnathostomata, gnathostomes (jawed fishes). They are currently considered to represent a paraphyletic Evolutionary grade, grade of various fish lineages Basal (phylogenetics), basal to extant tax ...

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 of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which have skeleto ...

, 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 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 251.902 Mya. It is the s ...

, 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 Biological process, process whereby an aquatic animal, aquatic organism exchanges Respiration (physiology), respiratory gases with water, obtaining oxygen from oxygen dissolved in water and excretion, excreting carbon ...

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

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

. 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 a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

. 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 Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of skin ...

the characteristic of three

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

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

{{Portal bar, Fish Gnathostomata Late Ordovician first appearances Extant Ordovician first appearances Taxa named by Charles Lucien Bonaparte Taxa described in 1836 Paraphyletic groups Obsolete vertebrate taxa