Shark

Sharks are a group of elasmobranch cartilaginous fishes known for by a ribless endoskeleton. Dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the division Selachii and are the sister group to the Batomorphi (rays and skates).

Some sources extend the term "shark" as an informal category including extinct members of Chondrichthyes (cartilaginous fish) with a shark-like shape and form, such as hybodonts. Shark-like chondrichthyans such as Cladoselache and Doliodus first appeared in the Devonian Period (419–359 million years). Though some fossilized chondrichthyan-like scales are as old as the Late Ordovician (458–444 million years ago).

The earliest confirmed modern sharks (Selachii) are known from the Early Jurassic around 200 million years ago. With the oldest known member being Agaleus, though records of true sharks may extend back as far as the Permian. Sharks range in size from the small dwarf lanternshark (Etmopterus perryi).

A deep sea species that is only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches about.