It is difficult to have sex in the ocean. Hydrodynamic drag on the penis, the trickiness of not getting seawater from not entering the uterus, and the basic difficulty of the mechanics of getting a penis into a vagina while swimming around make for a less than simple sexy situation. Mammals attempting a tumble in the watery jungle make it work within these environmental constraints, and the very fact that they are able to get it on has been a point of mysterious interest for scientists.

Enter the dolphin, an animal notoriously known for its voracious lovemaking. Bottlenose dolphins and the mechanics of their genitalia are the focus of a new paper presented Sunday at the annual meeting of the American Association of Anatomists in Chicago. Postdoctoral fellow Dara Orbach explains in the paper that she and co-author Patricia Brennan were able to determine the exact mechanics of dolphin copulation with a combination of specimen samples and computed tomography scans. This discovery, the researchers explain, provides both insight to the evolutionary forces that drove the formation of how dolphin genitals function and could be helpful for the advancement of captive breeding programs.

An image reconstructed from CT scans showing how the penis of the common bottle nose dolphin fits within the folds of a vagina.

Whales, dolphins, and porpoises have what Orbach describes “unusual vaginal folds, spirals, and recesses”, so the shape of the bottlenose dolphin penis has had to evolve in a way that lets it navigate through those folds and successfully inseminate the female. The way that the vagina is shaped is the primary force behind the morphological variation of most animal males — the twisty turns of the dolphin’s vagina means a twisty penis has to match.

“We demonstrate that particular anatomical landmarks are in contact during copulation and suggest that physical stimulation of these landmarks during artificial insemination may improve the probably of conception,” Orbach said in a statement. “Our research can also help predict which natural copulations will lead to fertilization, as males must sexually approach females at specific angles to optimize their genital alignment and penetration.”

Orbach and Brennan came to this conclusion after a three-part research study. The first part entailed excised male and female reproductive tracks from dead common bottlenose dolphins. The penises were mechanically inflated, formalin-fixed to remain rigid, and then inserted into frozen-thawed vaginas in “a position that approximates real intromission.” While this happened, their reproductive tracts were CT-scanned in order to have an image of how deeply the penis penetrated and what anatomical landmarks it comes into contact with.

With the information from the scans, the researchers also made silicone models of the interior of the vagina to further examine its shape. After pairing this data with video observations of actual free-swimming dolphins doing the deed, they concluded that the copulatory fit only happens because the penis is formed in a way that it fits through the folds.

The researchers claim that this knowledge not only answers the scientific question of how dolphin anatomy really works, but can eventually be useful in creating more successful captive breeding programs. These programs themselves are controversial, with some scientists claiming that they are necessary for conservation and research while others argue that cognitively advanced animals shouldn’t be captive in the first place.

Photos via Dara Orbach, Pexels