Hammerhead shark (Allie Caulfield / CC BY)
The hammerhead shark (Sphyrnidae) is characterized by a flattened and laterally extended cephalofoil that makes its head look like a hammer. The function of this shape is not fully understood, but sensory reception and maneuvering seem likely. Hammerhead sharks range from 0.9 meters (3 feet) to 6 meters (19.7 feet) in length. The scalloped, great, and smooth hammerheads have been reported to attack humans. As of 2013, 17 unprovoked incidents (all nonfatal) have been reported.