donny and the dolphin

All mammals have sex, but some mammals, like dolphins, have much weirder sex than others. And scientists are obsessed with studying marine mammal penises and vaginas to figure out the ins and outs of marine mammal mating, which is much more difficult than sex on land. After all, what’s a male dolphin to do if his penis is flopping around in the water, and how can a female keep seawater out of her uterus? The truly fascinating thing about dolphin genitals, it seems, is that they’re especially adapted for having complicated sex.

In a study published Wednesday in the journal Proceedings of the Royal Society B, some of those scientists used genitals from dolphins, seals, and porpoises to explore how vagina and penis anatomy work in harmony with — or in spite of — each other. The research of Dara Orbach of Dalhousie University in Nova Scotia, Diane Kelly of the University of Massachusetts, Mauricio Solano of Tufts University, and Patricia Brennan of Mount Holyoke College showed that vaginal anatomy exerts evolutionary pressure on penis shape, especially in the case of dolphins, whose vaginas contain numerous restrictive folds.

dolphin sex
Easier on land.

To enhance their understanding, the team performed the grisly task of collecting genital tracts submitted by other researchers who’d removed them from dolphins, seals, and porpoises that died natural deaths. (One of the most difficult things about understanding marine mammal genitals is the fact that it’s nearly impossible to watch the act close up.) The scientists then engorged the penises with nitrogen-pressurized saline, made silicon casts of the vaginas, and scanned 3D images of them. Here are some images that show these gruesome pairings:

dead dolphin dicks
These images show silicon vagina casts (smaller, green and blue shapes) and penises (bigger, brown shapes) from (a) harbour porpoises (Phocoena phocoena), (b) common bottlenose dolphins (Tursiops truncatus), (c) short-beaked common dolphins (Delphinus delphis) and (d) harbour seals (Phoca vitulina). As you can see, the engorged penis tip (4) of each species is similar in shape to the inside of the corresponding vagina.

These images show how penis shapes match up pretty closely to vagina anatomy. This may sound kind of obvious, but it’s actually been very difficult for scientists to observe what aquatic mammal sex looks like.

“Marine mammals offer important insights into the evolutionary forces that act on genital morphology because they have diverse genitalia and are adapted to aquatic living and mating,” write the authors.

But to get to the bottom of these animals’ sexual anatomies, the scientists had to actually fit the penises into the vaginas. So that’s what they did. They thawed vaginas, artificially erected penises with pressurized saline, and fit them together. Then the scientists took CT scans of the paired organs to see where the penises were making contact inside the vaginas. Here’s an example:

penises and vaginas
These CT scan reconstructions show aquatic mammal penises inside vaginas.  (a) harbour porpoises (P. phocoena), (b) common bottlenose dolphins (T. truncatus), (c) short-beaked common dolphins (D. delphis), and (d) harbour seals (P. vitulina) 

These images do more than let us see how the animals’ organs fit together. They also tell us how the organs don’t fit together. By better understanding how aquatic animals’ penises and vaginas function together, they gain insight into what positioning during sexual activity would have the highest rate of success.

“As cetaceans do not hold each other in place with appendages during copulation, and as females have the ability to evade males in a three-dimensional space, the body positioning of the male relative to the female during sexual approach may be a critical determinant of his fertilization success,” the researchers write. “Our data indicate the best genital shape correspondence and deepest possible penile penetration is a dorsal penis to ventral vagina orientation.”

In other words, dolphins doing it doggy-style — or “dolphin-style,” as we prefer to put it — have the highest chance of getting pregnant. Thank goodness for dolphin dick science.