Gnathostomata

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Gnathostomata Fossil range: Late Ordovician - Recent
Image:Orca-Schädel.jpg Gnathostomata are jawed vertebrates
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Infraphylum: Gnathostomata
Subgroups
Class Placodermi Superclass Chondrichthyes Microphylum Teleostomi Class Acanthodii Class Actinopterygii Parvophylum Tetrapodiiformes Class Sarcopterygii Superclass 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, reptiles, and amphibians, 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.^[1]

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

External links

• Tree of Life discussion of Gnathostomata
• The Gill Arches: Meckel's Cartilageca:Gnatostomat

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Acknowledgement and Attribution Regarding Sources of Content

Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .