Boschung, Herbert T. Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama.
Last reviewed:January 2020
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A superclass of the subphylum Vertebrata consisting of animals that possess jaws. The superclass Gnathostomata comprises the jawed vertebrates (subphylum Vertebrata, phylum Chordata). In other words, gnathostomes are animals with jaws, involving a vertical biting that developed from modified gill arches. The gnathostomes are characterized further by a notochord (an elongated dorsal cord of cells that is the primitive axial skeleton in all chordates) that is present in the ontogeny of all lineages, but replaced by vertebral centra (the main bodies of vertebrae) in most taxa; limb girdles (secondarily lost in some forms) that support paired appendages in all but the most primitive taxa; myelinated neurons; an adaptive immune system; intrinsic eye muscles; a sperm duct linked to the urinary system; and a distinct cerebellum. In addition, early fossil forms possessed a bony exoskeleton that was lost in the higher lineages. Some of the characters were carried over from the primitive superclass Agnatha (jawless vertebrates), but jaws and paired appendages are unique to members of the Gnathostomata. See also: Animal evolution; Chordata; Jawless vertebrates; Vertebrata
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