It doesn't get much better than a narwhal. These bizarre creatures are a species of toothed whale, and the males have evolved an extra long left canine tooth that can grow up to 2.7 metres (9 feet) long, bursting through the upper lip and protruding from the head like the horn of a unicorn.

The mystery of why these 'horns' exist has led scientists to a number of possible functions - they appear to signal testicle size to the females, and they're sometimes used in battles like a fencing foil. That tooth can also be used for navigation - and now scientists have discovered that it gives narwhals the most directional sonar of any species on Earth.

A team led by Kristin Laidre, an ecologist at the University of Washington, decided to investigate the echolocation skills of narwhals by placing waterproof sound-recorders called hydrophones at 11 pack ice sites in Baffin Bay, West Greenland.