Dolphins ‘Smile’ When They Play Together, Research Footage Reveals

Just like humans, a dolphin’s face can’t help but give away when it’s having a good time. Scientists in Italy have found that bottlenose dolphins (Tursiops truncatus) make a distinct open mouth gesture when playing with others. The display is likely akin to smiling and laughing in humans and suggests that these playful facial expressions are deeply rooted in the shared ancestral past of mammals, the researchers say.

Despite being marine animals, bottlenose dolphins are known for having a lot in common with humans, from using “baby talk” with their infants to being incredibly social with each other (and humans). Much of that sociability is expressed in the play that they routinely engage in. But as study researchers Elisabetta Palagi and Livio Favaro began to study how captive dolphins played, they soon noticed something interesting happening with the animals’ faces.

“When in front of the pool and after recording the first videos we realized that dolphins emitted prolonged open mouth displays while playing, and we did not see a similar behavior in any other context. So we decided that the topic was important to study,” Palagi, an evolutionary biologist at the University of Pisa who has long studied play in primates, told Gizmodo.

To confirm their initial observations, the team extensively recorded dolphins while they were playing in pairs, playing with their human trainers, or simply entertaining themselves. Palagi and her team only documented a single instance of the open mouth display when the dolphins were alone, but many more when the dolphins were playing with a pal, particularly other dolphins.

Of the 1,288 open mouth events they recorded, 92% occurred during paired dolphin sessions. Most (89%) also happened when the dolphins were clearly able to see one another. And when the dolphins saw another dolphin “smile” at them, they quickly returned back the same gesture about a third of a time. The team’s findings were published Wednesday in the journal iScience.

“In our research, we’ve uncovered the presence of a distinct facial display, the Open Mouth, in bottlenose dolphins,” Palagi said. “This discovery sheds new light on how dolphins use subtle facial cues during social play.”

Dolphin communication is plenty varied. They’re thought to have one of the most intricate vocal systems in the animal world, according to Palagi, complete with high-pitched whistles that are used for social interaction and to identify individual dolphins. These vocal gestures are especially important when the animals are traveling through murky water. But when the dolphins are in clear waters or close to one another, they switch more to visual communication, making facial expressions all the more important for quick two-way exchanges, Palagi says.

The team also appears to be the first to discover that dolphins can recognize and rapidly mimic the playful open mouth gestures of their playmates, perhaps similar to how humans can burst into smiles and laughter when we see our friends having fun, too. It’s possible that the dolphins were simply making the same faces by coincidence, but Palagi notes that the dolphins were much more likely to mimic when they clearly saw the other dolphin’s original expression, undermining that alternative explanation.

While dolphins may not have as wide a range of facial expressions as primates or other land-based social animals, they are still mammals. And given how commonly these sorts of playful gestures appear across different mammal species, it’s likely that they first emerged in our ancestors quite a long time ago, and possibly more than once.

“Though we are still unraveling the evolutionary origins of play and how animals fine-tune their playful behaviors, one thing is clear: open-mouth signals and rapid mimicry appear repeatedly across the mammal family tree. This suggests that visual communication has played a crucial role in shaping complex social interactions, not only in dolphins but in many species over time,” Palagi said. “In short, human laughing can have very ancient origins that probably evolved several times in the fantastic tree of life!

Palagi says more research should be done to investigate how other animals, particularly the mammals more closely to related to dolphins like deer, hippos, and other artiodactyls, communicate while playing. There should also be more study into how dolphins use their voices while playing and how their play differs between other dolphins and human caretakers, she adds.