High Quality Content by WIKIPEDIA articles! Sharks belong to the superorder Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes. The Elasmobranchii also include rays and skates; the Chondrichthyes also include Chimaeras. It is currently thought that the sharks form a polyphyletic group: in particular, some sharks are more closely related to rays than they are to some other sharks. The first sharks appeared in the oceans 350 to 400 million years ago. Most of the species we know today are as old as the Jurassic period.