Comprising all vertebrates with upper and lower jaws: Chondrychthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia. These animals usually have paired olfactory organs and nostrils and paired limbs.
Gnathostomes belong either to the Fishes or to the Tetrapods (animals with four limbs, albeit that some of the limbs may be reduced or lost