Watch: Bottlenose dolphins ‘smile’ at each other while playing

They are known for being playful and performing impressive underwater acrobatics, but now scientists have discovered bottlenose dolphins “smile” during play.

Researchers have found Tursiops truncate have an “open mouth” expression that they use to communicate with each other during play, much like a smile in humans.

Researchers recorded 22 captive bottlenose dolphins while they were playing in pairs and while playing with their human trainers.

Analysing 80 hours of video involving 837 play sessions, the researchers found that the dolphins used the open mouth expression when playing with each other but not when playing with humans or playing on their own.

Out of a total of 1,288 open mouth events during social play sessions, 92 percent of these events occurred during dolphin-dolphin play sessions, the scientists said.