Gnathostomata

Information about Gnathostomata

Gnathostomata
Fossil range: Late Ordovician - Recent

Gnathostomata are jawed vertebrates

Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Infraphylum:	Gnathostomata

Subgroups

Class Placodermi
Superclass Chondrichthyes
Microphylum Teleostomi
Class Acanthodii
Class Actinopterygii
Parvophylum Tetrapodiiformes
Class Sarcopterygii
Nanophylum Tetrapoda
Class Amphibia
(Unranked) Amniota
Class Sauropsida
Class Aves
Class Synapsida
Class Mammalia

Gnathostomata is the group of vertebrates with jaws.

The group is traditionally a superclass, including the familiar classes of fish, birds, mammals, and so forth, and a sister group of the jawless vertebrates Agnatha. However, recent genetic studies are causing a reassessment of Gnathostomata as a grouping.

New fossil founds suggests thelodonts as the closest relatives of the Gnathostomata.^[1]

It is believed that the jaws evolved from anterior gill 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.^[2]

Other distinguishing characteristics of living gnathostomates are the myelin sheathes of neurons, and an adaptive immune system.

The Gnathostomata first appeared in the Ordovician period and became common in the Devonian period.

Taxonomy and phylogeny

Subphylum Vertebrata ├─(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 Mammalia (mammals) Note: lines show evolutionary relationships.

References

1. ^ Mark V. H. Wilson & Michael W. Caldwell (1993-02-04). New Silurian and Devonian fork-tailed 'thelodonts' are jawless vertebrates with stomachs and deep bodies. nature. Retrieved on 2007-08-22.
2. ^ Susan Turner and Randall F. Miller (June 2005). New Ideas About Old Sharks. American Scientist. Retrieved on 2007-08-22.

External links

The Late Ordovician, also called the Upper Ordovician by geologists, is the third epoch of the Ordovician period.

At this time Western and Central Europe and North America collided to form Laurentia, while glaciers built up in Gondwana, which was positioned over the
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Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. Scientific classification also can be called scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis.
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Chordata
Bateson, 1885

Typical Classes

See below

Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates.
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Vertebrata
Cuvier, 1812

Classes and Clades

See below
Vertebrates are members of the subphylum Vertebrata (within the phylum Chordata), specifically, those chordates with backbones or spinal columns.
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Placodermi
McCoy, 1848

Orders

Antiarchi †
Arthrodira †
Brindabellaspida †
Petalichthyida †
Phyllolepida †
Ptyctodontida †
Rhenanida †
Acanthothoraci †
?Pseudopetalichthyida †
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Chondrichthyes
Huxley, 1880

Subclasses and Orders

See text.

The Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage rather than bone.
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Teleostomi
C. L. Bonaparte, 1836

Classes and Clades

Acanthodii
Euteleostomi

Osteichthyes
Actinopterygii
Sarcopterygii
Tetrapoda

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Acanthodii

Orders

Climatiiformes
Ischnacanthiformes
Acanthodiformes

Acanthodii (sometimes called spiny sharks) is a class of extinct fishes, having features of both bony fish (Osteichthyes) and cartilaginous fish (Chondrichthyes).
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Actinopterygii
Klein, 1885

Subclasses

Chondrostei
Neopterygii
See text for orders.
The Actinopterygii (the plural form of Actinopterygius) comprise the class of the ray-finned fishes.
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Sarcopterygii

Subclasses

Coelacanthimorpha - Coelacanths
Dipnoi - Lungfishes
Tetrapodomorpha - Tetrapods

Sarcopterygii (from Greek sarx, flesh, and pteryx
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Tetrapoda
Broili, 1913

Classes

Amphibia
Aves
Mammalia
Sauropsida (Reptilia)
Synapsida

Tetrapods (Greek tetrapoda, Latin quadruped
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Amphibia
Linnaeus, 1758

Subclasses and Orders

   Order Temnospondyli - extinct
Subclass Lepospondyli - extinct
Subclass Lissamphibia
   Order Anura
   Order Caudata
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Amniota
Haeckel, 1866

Living subgroups

See text

The amniotes are a group of tetrapod vertebrates that include the Synapsida (mammals and mammal-like reptiles) and Sauropsida (reptiles and dinosaurs, including birds).
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Sauropsida ("lizard-face") is a group of amniotes that includes reptiles, dinosaurs, and birds. Among amniotes, sauropsida is distinguished from theropsida ("beast-face"), also called synapsids.

Taxonomy

Classification to order level, after Benton, 2004.
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Aves
Linnaeus, 1758

Orders

About two dozen - see section below

Birds (class Aves) are bipedal, warm-blooded, egg-laying vertebrate animals.
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Synapsida *
Osborn, 1903

Orders & Suborders

'''Order Pelycosauria *
Suborder Caseasauria
Suborder Eupelycosauria *
Order Therapsida

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Mammalia
Linnaeus, 1758

Subclasses & Infraclasses

Subclass †Allotheria*
Subclass Prototheria
Subclass Theria

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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.
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class is the rank in the scientific classification of organisms in biology below Phylum and above Order.

For example, Mammalia is the class used in the classification of dogs, whose phylum is Chordata (animals with notochords) and order is Carnivora (mammals that eat meat).
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Mammalia
Linnaeus, 1758

Subclasses & Infraclasses

Subclass †Allotheria*
Subclass Prototheria
Subclass Theria

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Agnatha (Greek, "no jaws") is a paraphyletic superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. Agnatha have existed since the Cambrian, and continue to live in modern times.
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Thelodonti ("Nipple teeth") were very similar to the fish of the classes Heterostraci and Anaspida, though the thelodonts were covered with distinctive, small, spiny scales, which are their most common fossils.
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A gill is a respiration organ that functions for the extraction of oxygen from water and the excretion of carbon dioxide. Unlike many small aquatic animals, which can absorb oxygen through the entire surface of their bodies, more complex aquatic organisms have gills specially
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Buccal pumping is a method of respiration using the throat muscles. Animals using this method will typically move the floor of the mouth or throat in a rhythmic manner that is externally apparent.

This method has several stages.
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Myelin is an electrically insulating phospholipid layer that surrounds the axons of many neurons. It is an outgrowth of glial cells: Schwann cells supply the myelin for peripheral neurons while oligodendrocytes supply it to those of the central nervous system.
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Gnathostomata

Information about Gnathostomata

Taxonomy and phylogeny

References

External links

Taxonomy