Some scientists estimate that sharks have been swimming the deep blue seas relatively unchanged for hundreds of millions of years. They also have electrosensitivity, which allows them to track prey by the electric fields that all animals generate. Bet you didn't know . . . All sharks are protected by tough hides that are studded with tooth-like growths called denticles. They live all over the world in both warm and cold regions of the ocean, as well as rivers and fresh water.
Most sharks bear live young, although some species lay eggs with protective horny shells.
The largest are about 15' in length. Oddly enough, their eyes and ears are on the outside tips of their T-shaped heads. Hammerheads are sometimes seen swimming in schools. Approximately 20' long and 1,000 pounds in weight. They use their long forked tails to sweep prey in front of them, and to frighten fish by slapping the water.