font settings

Font Size: Large | Normal | Small
Font Face: Verdana | Geneva | Georgia

ZipcodeZoo.com needs to raise another $12,000 in donations by January 1 to continue operation in 2009.
If we cannot meet this goal, this site will go offline January 1. Please click here to donate

gnathostomata

(Infraphylum)

Overview

[ Back to top ]

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 bonyplates 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

[ Back to top ] 
Subphylum Vertebrata+-(unranked) Gnathostomatomorpha+-Infraphylum Gnathostomata      +-Class Placodermi - extinct (armored gnathostomes)      +Microphylum Eugnathostomata (true jawed vertebrates)         +-Class Chondrichthyes (cartilaginous fish)         +-(unranked) Teleostomi (Acanthodii & Osteichthyes)    +-Cl    ass 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.

Photos

[ Back to top ]

Taxonomy

[ Back to top ]

The Infraphylum gnathostomata is a member of the Subphylum Vertebrata. Here is the complete "parentage" of Gnathostomata:

The Infraphylum gnathostomata is further organized into finer groupings including:

Classes

[ Back to top ]

Actinopterygii

The Actinopterygii (the plural form of Actinopterygius) comprise the class of the ray-finned fishes. [more]

Agnatha

[more]

Amphibia

Amphibians (class Amphibia), such as frogs toads salamanders newts and gymnophiona, are cold-blooded animals that metamorphose from a juvenile, water-breathing form to an adult, air-breathing form. Typically, amphibians have four limbs. Unlike other land animals (amniotes), amphibians lay eggs in water, as their fish ancestors did. Amphibians are superficially similar to reptiles. [more]

Aves

[more]

Chondrichthyes

Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage rather than bone. They are divided into two subclasses: Elasmobranchii (sharks, rays and skates) and Holocephali (chimaera, sometimes called ghost sharks). [more]

Colpodea

. [more]

Crustacea

The crustaceans (Crustacea) are a large group of arthropods, comprising almost 52,000 described species , and are usually treated as a subphylum . They include various familiar animals, such as crabs, lobsters, crayfish, shrimp and barnacles. The majority of them are aquatic, living in either marine or fresh water environments, but a few groups have adapted to life on land, such as terrestrial crabs, terrestrial hermit crabs and woodlice. Crustaceans are among the most successful animals, and are as abundant in the oceans as much as insects are on land. Over half of animals in the world are marine copepod crustaceans. The majority of crustaceans are also motile, moving about independently, although a few taxonomic units are parasitic and live attached to their hosts (including sea lice, fish lice, whale lice, tongue worms, and Cymothoa exigua, all of which may be referred to as "crustacean lice"), and adult barnacles live a sessile life — they are attached headfirst to the substrate and cannot move independently. Although most crustaceans are small, their morphology varies greatly and they include such large animals as lobsters 70 cm long and spider crabs with a leg span of nearly 4 m. [more]

Gastropoda

The class Gastropoda or the gastropods, also previously known as gasteropods, or univalves, and more commonly known as snails, are the most diversified class belonging to the phylum of mollusks, with 60,000-75,000 known living species. This class of animals is second only to insects in its number of known species. [more]

Mammalia

Mammals (class Mammalia) are a class of vertebrate animals characterized by the presence of sweat glands, including sweat glands modified for milk production, hair, three middle ear bones used in hearing, and a neocortex region in the brain. [more]

Osteichthyes

Osteichthyes (IPA: /??sti?'?k?i?z/), also called bony fish, are a taxonomic Class of fish that includes the ray-finned fish (Actinopterygii) and lobe finned fish (Sarcopterygii). The split between these two classes occurred around 440 mya. [more]

Placodermi

The Placodermi were a class of armoured prehistoric fishes, 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 among the first jawed fishes; their jaws likely evolved from the first of their gill arches. A 380 millions year old fossil of one of the species represents the oldest-known example of live birth. [more]

Reptilia

Reptiles are air-breathing, cold-blooded vertebrates that have skin covered in scales as opposed to hair or feathers. They are tetrapods (having or having descended from vertebrates with four limbs) and amniotes, whose embryos are surrounded by an amniotic membrane. Modern reptiles inhabit every continent with the exception of Antarctica, and are represented by four living orders: [more]

Sauropsida

Reptiles are air-breathing, cold-blooded vertebrates that have skin covered in scales as opposed to hair or feathers. They are tetrapods (having or having descended from vertebrates with four limbs) and amniotes, whose embryos are surrounded by an amniotic membrane. Modern reptiles inhabit every continent with the exception of Antarctica, and are represented by four living orders: [more]

Secernentea

Secernentea are a class of nematodes characterised by numerous caudal papillae and an excretory system possessing lateral canals. They have no circulatory or respiratory system. [more]

Synapsida

[more]

At least 4 species and subspecies belong to the Class synapsida.

More info about the Class synapsida may be found here.

References

[ Back to top ]
[ Back to top ]
  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.

Sources

[ Back to top ]
Last Revised: June 23, 2008