Defying Evolution: Observations of a Mouth-Breathing Bottlenose Dolphin (Tursiops truncatus)

In the Adriatic Sea, a female common bottlenose dolphin named “Boa” was observed on 19 occasions between 2009 and 2019, inhaling via her mouth for every observed respiration. We provide some explanations for the potential cause of this behaviour using existing evidence. Boa appeared to be in good physical shape and displayed behaviour similar to other individuals. She mothered three calves, raising at least one to independence successfully. Because she lived a normal life, we believe she could vocalise and echolocate. Boa may have been forced to breathe through her mouth to deal with internal injuries, occlusion, or disease. Of the potential causes, an occlusion of the upper respiratory tract seems more likely than a perforation or permanent dislocation of the larynx. An occlusion could result from disease, a congenital disorder, and/or wrongly ingested or inhaled food items or foreign materials. To breathe via the mouth, Boa must have been able to circumvent the separation of the respiratory tract from the oral cavity. By relaxing the respiratory muscles, particularly the palatopharyngeus, she could have used the negative pressure of the lungs to pull in air from the oropharynx into the upper respiratory tract. The true cause of Boa’s condition will probably never be discovered.