Dolphins can recognise family and friends by tasting their urine.
Researchers have discovered that unusual sensory cells on the tongue help the mammals detect individual tastes of other animals in the sea.
The dolphins were found to explore urine samples for longer if they came from a creature they recognised or when hearing a unique dolphin whistle.
Professor Vincent Janik, from St Andrews University in Scotland, said: "This shows not only that they can tell animals apart by taste but also recognise animals across their senses, hinting at a complex representation of familiar animals in a dolphin's brain."
His colleague Jason Bruck, from Stephen F. Austin State University in Texas, revealed that the findings took him by surprise.
He said: "It was a shot in the dark. And I was not expecting it to work, to be honest."