A shark's weight wildly varies by species. The world's smallest shark, the dwarf lantern shark, is able to fit in a person's hand, while the whale shark can reach over 40 feet in length and can weigh over 47,000 pounds.
Sharks are cartilaginous fish closely related to skates and rays. Fossil records indicate that sharks have existed since the Devonian Period. Although they are ancient animals, sharks have changed very little in their history, with the exception of improvements to swimming and feeding. Most sharks eat fish, although some species have physiological modifications for their respective diets. Filter-feeding sharks, such as the whale shark and the megamouth shark, ingest and expel large quantities of water in order to feed on plankton.