Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago. Since that time, sharks have diversified into 440 species, ranging in size from the small dwarf lantern shark, a deep sea species of only 17 centimeters in length, to the whale shark, the largest fish, which reaches approximately 12 meters and which feeds only on plankton, squid, and small fish by filter feeding.