Sharks are elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins
Well okay then! I know there are lots of different species as well -- and that they definitely get a bad rap!
Today's shark is classified as  clade Selachimorpha which is not too different from ray
As in a manta ray? I didn't realize they were related in any way.
Sharks  and their history  date back to more than 420 million years ago
And where were the first fossils found?
eugenedontidans.
Under this broader definition, the earliest known sharks date back to more than 420 million years ago. Acanthodians are often referred to as "spiny sharks"; though they are not part of Chondrichthyes proper, they are a paraphyletic assemblage leading to cartilaginous fish as a whole. Since then, sharks have diversified into over 500 species. They range in size from the small dwarf lanternshark ("Etmopterus perryi"), a deep sea species of only in length, to the whale shark ("Rhincodon typus"
Shark
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as "Cladoselache" and "Xenacanthus", as well as other Chondrichthyes such as the holocephalid