Female dolphins are known to be highly social and engage in all sorts of sexual behavior.

In addition to mating with male dolphins, female bottlenose dolphins are, for instance, known to masturbate and also rub each other's clitoris with snouts, flippers, and flukes, suggesting the acts are pleasurable for them.

For instance, female koalas sometimes mount other females, while male Amazon river dolphins have been known to penetrate each other's blowholes.

Despite this abundance of behavioral evidence, there have been very few academic studies of the clitoris and female sexual pleasure in nature, according to Patricia Brennan, a marine biologist at Mount Holyoke College in Massachusetts and a co-author of the new study.

"This has left us with an incomplete picture of the true nature of sexual behaviors," she said.

"I think it makes some people uncomfortable." As for why male sexuality has been studied more frequently than female sexuality (in both humans and animals), that's partly due to inherent biases—until quite recently, the vast majority of scientists were men.

"A male penis is just sticking out there," Brennan said.

Male ducks are famous for their spectacularly long corkscrew penises, "but nobody had thought to look at the vagina of a duck to see how it would interact with those weird penises," she said.

If the morphology of the dolphin clitoris had shared features with a human clitoris, that would suggest functionality that may provide pleasure during these sexual encounters.