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Hammerhead sharks appeared about 20 million years ago with a number of species surviving today. The width of the cephalofoils (winged head) of each species varies considerably. Greater width seems to provide the better binocular vision common to predators compared to other shark families. The cephalofoil also gives hammerheads the maneuverability to capture quick, darting prey compared to other sharks that rely on speed to chase down prey.

Jeremy Wade returns to Australia's predator-packed Fitzroy River in search of one of the world's rarest and least known fish - the Northern River Shark. It's so elusive that only twenty have ever been caught.