Zweifel, Richard G. Department of Herpetology, American Museum of Natural History, New York, New York.
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The superclass of the subphylum Vertebrata whose members typically possess limbs, including all forms above fishes. The members of the superclass Tetrapoda (subphylum Vertebrata, phylum Chordata) constitute the limbed vertebrates and their descendants (which may have evolved into limbless forms). The animals making up the Tetrapoda (tetrapods) stand in contrast to the fishes (the informal grouping, Pisces), whose members have fins. The tetrapods typically live part or all of their lives on land, whereas the members of the Pisces live in water. The classes of the Tetrapoda are Amphibia (frogs, toads, salamanders, and caecilians), Reptilia (snakes, lizards, turtles, and crocodiles and their kin), Aves (birds), and Mammalia (mammals). The term Tetrapoda is derived from Greek words meaning “four feet,” but there are tetrapods that have only two limbs or none at all, such as some amphibians and reptiles. These forms, however, have evolved from four-footed ancestors. Ongoing research continues to investigate the origins of tetrapods, and remarkable fossil specimens (for example, the Devonian Tiktaalik roseae) are providing new clues into the exact nature of this evolutionary process. See also: Amphibia; Animal evolution; Aves; Devonian missing link; Mammalia; Pisces (zoology); Reptilia; Tetrapod origins
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