It turns out dolphins can express positive emotions in ways that look a lot like human smiles—mainly with a particular facial pose: their open mouths, often called their “beaks.” Biologists say dolphins don’t just appear cheerful; they genuinely smile at each other. They also seem to pass that cheer along to their friends. Researchers at the University of Pisa found that bottlenose dolphins (Tursiops truncatus) in captivity use these open-mouth expressions as friendly signals. The team suggested that when one dolphin copies another’s open mouth during play, it promotes a friendly interaction rather than an aggressive one.
“We discovered a characteristic facial expression in bottlenose dolphins—the open mouth—and observed that dolphins can mimic the facial expressions of others,” said evolutionary biologist Elizabeth Palagi, the lead author of the study.
What did the researchers find? The open mouth that signals a smile—seen in dogs, primates, horses, and humans—appears to be a common cue for playfulness. That expression helps animals and people show a positive mood and avoid conflicts, Science Alert reported. Until now, many assumed dolphins couldn’t express emotions through facial muscles; their visual communication hadn’t been deeply studied. The Pisa team was the first to closely examine the smiles of these marine mammals.
The researchers focused on play, which the team found cuts across ages. Palagi and her colleagues analyzed 80 hours of video showing 22 dolphins playing in captivity across four social groups. They found that just one dolphin opened its mouth during solitary play, while most bottlenose dolphins did so consistently during social games like chasing or light sparring. The researchers emphasized that these interactions were not aggressive. Typically, dolphins chase one another, nip playfully, or bump their beaks together without trying to cause harm.
During these interactions, 90 percent of the players opened their mouths in what looks like a smile, and in about one-third of cases they received an immediate smile in return from a playmate. The data do not rule out the possibility that dolphins use open-mouth displays in other situations, but the results support the idea that smiling bottlenose dolphins send friendly social signals. “The open-mouth expression likely evolved from biting, where a biting sequence was interrupted, leaving only the ‘intention to bite’ without contact,” Palagi explained. She added that similar rapid mimicry shows up in some carnivores, such as meerkats and sun bears.
The study was done only with dolphins in captivity, so it’s unclear how often they use this positive signaling in the wild.
“While we are far from understanding the evolutionary origins of play and the ability of animals to fine-tune their play sessions, the widespread presence of open-mouth signals and rapid mimicry across mammals suggests these visual mechanisms play an important role in complex communication,” the team wrote. The study was published in the journal iScience.
