9Great white, bull, and tiger sharks are some of today's most talked-about sharks. But have you met the sharks of yesterday? Each prehistoric shark had its own amazing--and sometimes strange--features. The scissor-tooth shark had teeth in a spiral shape. The giant megalodon was about three times the size of a great white. One small prehistoric shark had a big dorsal fin in the shape of an ironing board! Readers will gobble up all the facts about these early ocean hunters and learn how they compare to modern sharks.