Class Chondritchthyes

The Chondrichthyes are considered the oldest existing jawed-vertebrates related to bony vertebrates (Osteichthyes). The earliest dated Chondricthyes fossils are from the Silurian period. The two subclasses of Chodrichtyes, Holocephali and Elasmobranchii are believed to have diverged 410 mya and become more diversified in the Devonian.

Chondrichthyes live mostly in marine locations but few species live in freshwater. Some defining characteristics of Chondrichthyes are internal fertilization by the use of pelvic claspers, heterocercal tails, placoid scales, cartilage skeletons, teeth unattached to jaws, and the absence of swim bladders.

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