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Gnathostomata
 
 
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Gnathostomata is the group of vertebrate
Vertebrate

Vertebrates are members of the subphylum Vertebrata, chordates with Vertebras or Vertebral columns. The grouping sometimes includes the hagfish, which have no vertebrae, but are genetically quite closely related to lampreys, which do have vertebrae....
s with jaw
Jaw

The jaw is either of the two opposable structures forming, or near the entrance to the mouth.The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of most animals....
s.

The group is traditionally a superclass, broken into two top level groupings; cartilaginous fish, and all other members, including the familiar classes of bony fish, bird
Bird

Birds are wing, Bipedalismal, endothermic , vertebrate animals that lay egg . There are around 10,000 living species, making them the most numerous tetrapod vertebrates....
s, mammal
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
s, reptile
Reptile

Reptiles, or members of the class Reptilia, are air-breathing, cold-blooded vertebrates that have skin covered in scale as opposed to hair or feathers....
s, and amphibian
Amphibian

Amphibians , such as frogs, toads, salamanders, newts and caecilians, are cold-blooded animals that metamorphose from a juvenile, water-breathing form to an adult, air-breathing form....
s. It is a sister group of the jawless vertebrates Agnatha
Agnatha

Agnatha is a class or superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. Many recent textbooks regard the group as paraphyletic but recent molecular data, both from rRNA and from mtDNA strongly supports living agnathans as monophyletic....
.

Recent genetic studies are causing a reassessment of Gnathostomata as a grouping.

New fossil finds suggests thelodonts
Thelodonti

There is much debate over whether the clade of Palaeozoic fish known as the Thelodonti represent a Monophyly, or disparate stem groups to the major lines of Agnatha and Gnathostome....
 as the closest relatives of the Gnathostomata.

It is believed that the jaws evolved from anterior gill
Gill

A gill is an anatomical structure found in many aquatic ecosystem organisms. It is a respiration organ whose function is the extraction of oxygen from water and the excretion of carbon dioxide....
 support arches that had acquired a new role, being modified to pump water over the gills by opening and closing the mouth more effectively — the buccal pump mechanism.






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Encyclopedia


Gnathostomata is the group of vertebrate
Vertebrate

Vertebrates are members of the subphylum Vertebrata, chordates with Vertebras or Vertebral columns. The grouping sometimes includes the hagfish, which have no vertebrae, but are genetically quite closely related to lampreys, which do have vertebrae....
s with jaw
Jaw

The jaw is either of the two opposable structures forming, or near the entrance to the mouth.The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of most animals....
s.

The group is traditionally a superclass, broken into two top level groupings; cartilaginous fish, and all other members, including the familiar classes of bony fish, bird
Bird

Birds are wing, Bipedalismal, endothermic , vertebrate animals that lay egg . There are around 10,000 living species, making them the most numerous tetrapod vertebrates....
s, mammal
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
s, reptile
Reptile

Reptiles, or members of the class Reptilia, are air-breathing, cold-blooded vertebrates that have skin covered in scale as opposed to hair or feathers....
s, and amphibian
Amphibian

Amphibians , such as frogs, toads, salamanders, newts and caecilians, are cold-blooded animals that metamorphose from a juvenile, water-breathing form to an adult, air-breathing form....
s. It is a sister group of the jawless vertebrates Agnatha
Agnatha

Agnatha is a class or superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. Many recent textbooks regard the group as paraphyletic but recent molecular data, both from rRNA and from mtDNA strongly supports living agnathans as monophyletic....
.

Recent genetic studies are causing a reassessment of Gnathostomata as a grouping.

New fossil finds suggests thelodonts
Thelodonti

There is much debate over whether the clade of Palaeozoic fish known as the Thelodonti represent a Monophyly, or disparate stem groups to the major lines of Agnatha and Gnathostome....
 as the closest relatives of the Gnathostomata.

It is believed that the jaws evolved from anterior gill
Gill

A gill is an anatomical structure found in many aquatic ecosystem organisms. It is a respiration organ whose function is the extraction of oxygen from water and the excretion of carbon dioxide....
 support arches that had acquired a new role, being modified to pump water over the gills by opening and closing the mouth more effectively — the buccal pump mechanism. The mouth could then grow bigger and wider, making it possible to capture larger prey. This close and open mechanism would with time become stronger and tougher, being transformed into real jaws.

Placoderms used sharp bony plates as teeth instead, and newer research indicates the jaws in placoderms evolved independently of the rest of the remaining gnathostomates.

Other distinguishing characteristics of living gnathostomates are the myelin
Myelin

Myelin is an electrically-insulating dielectric material that forms a layer, the myelin sheath. Usually, myelin surrounds only the axon of a neuron....
 sheathes of neuron
Neuron

Neurons are responsive cell in the nervous system that process and transmit information by electrochemical Signal . They are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves....
s, and an adaptive immune system
Immune system

An immune system is a collection of biological processes within an organism that protects against disease by identifying and killing pathogens and tumour cells....
.

The Gnathostomata first appeared in the Ordovician period
Ordovician

The Ordovician is a geologic period, 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 ....
 and became common in the Devonian period
Devonian

The Devonian is a geologic period of the Paleozoic era spanning from . It is named after Devon, England, where rocks from this period were first studied....
.

Taxonomy and phylogeny

Subphylum Vertebrata +-(unranked) Gnathostomatomorpha +-Infraphylum Gnathostomata +-Class Placodermi
Placodermi

The Placodermi were a Class of armoured prehistoric fish, known from fossils, which lived from the late Silurian to the end of the Devonian Period....
 — extinct (armored gnathostomes) +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
Teleostomi

Teleostomi is a clade of Gnathostomata that includes the tetrapods, osteichthyes, and the wholly extinct Acanthodii 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....
 (Acanthodii & Osteichthyes) +-Class Acanthodii
Acanthodii

Acanthodii is a class of extinct fishes, having features of 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 taxonomy group of fish that includes the ray-finned fish and lobe finned fish . The split between these two classes occurred around 440 mya ....
 (bony fish) +-Class Actinopterygii
Actinopterygii

The Actinopterygii constitute the Class of the ray-finned 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 the class Sarcopterygii....
 (ray-finned fish) +-Class Sarcopterygii
Sarcopterygii

Sarcopterygii - Crossopterygii is traditionally the class of fleshy-finned, lobe-finned fishes, consisting of lungfish, and coelacanths....
 (lobe-finned fish) +Superclass Tetrapoda +-Class Amphibia (amphibians) +(unranked) Amniota (amniotic egg) +-Class Sauropsida
Reptile

Reptiles, or members of the class Reptilia, are air-breathing, cold-blooded vertebrates that have skin covered in scale as opposed to hair or feathers....
 (reptiles or sauropsids) ¦ +-Class Aves
Bird

Birds are wing, Bipedalismal, endothermic , vertebrate animals that lay egg . There are around 10,000 living species, making them the most numerous tetrapod vertebrates....
 (birds) +-Class Synapsida +-Class Mammal
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
ia (mammals)   Note: lines show evolutionary relationships.

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