The ventral (or under) side of the
animal presents a number of important anatomical features. About halfway between the head and flukes, a navel (or belly
button) may be found. This is the remaining fetal connection point with the mother via the placenta and umbilical cord so
common to all mammals. In the photograph below of a male dolphin, the navel is about the size of a half dollar and appears
in the upper third of the picture.
Another prominent feature is the urogenital and anal openings and,
if female, the mammary slits. A male may have small, vestigial mammary slits. But they are not as prominent as in the female.
Male Versus Female
Determining male from female Atlantic Bottlenose Dolphin is not as
difficult as one might initially suspect. In the female, the urogenital and anal slits are one in the same – a long
slit extending ventrally from just past the dorsal fin to the center of the peduncle. The male’s urogenital and anal
slits are slightly separate. BUT, the most prominent feature distinguishing gender is the presence of 3 inch long mammary
slits on either side and parallel to the urogenital/anal opening of the female. Under each of these two mammary slits may
be found a left and right mammary gland, internally located so as to avoid drag or resistance when the animal is swimming.
Typically, adult males will weight 25% more than adult females.
This is a photograph of the underside of a female Atlantic Bottlenose Dolphin.
The single urogenital/anal opening is easily seen, as are the two mammary slits, one to each side of this opening. Thus, the
female dolphin is said to resemble a "divide sign" in appearance.
This photograph of the male's underside shows his urogenital opening with a separate opening for the anus. Thus,
we say the male resembles an "exclamation mark" in appearance.
According to the Dolphin Research Center in Marathon, Florida, dolphins are indiscriminately amorous, engaging
in a number of sexual behaviors with other dolphins and with inanimate objects as a means of developing those sexual and social
skills needed as adults. It is believed that males need more time to practice their sexual behavior skills than do females.
In this video a young (6 year old) male dolphin is carrying a Frisbee on his erect reproductive organ
(penis). With a young dolphin, an erection without "cause" is common. In fact, an erection is a voluntary action for male
dolphins. While swimming, the erect organ faces forward to facilitate insertion into the female urogenital opening during
intercourse. Little to no stimulus is required for ejaculation to occur. This is to the dolphin's advantage because
male-to-female contact during mating is not lengthy, amounting to only a few seconds. If such contact were lengthy it
could divert the attention of the pair, decreasing their chances of detecting approaching predators. Rapid ejaculation
also allows for the easy collection of semen samples from captive dolphins, an important part of the health assessment process.
It is believed that ejaculation is a voluntary process in dolphins.
Understanddolphins.com contains information condensed from a number of reputable technical sources,
peer reviewed journal articles, and respected dolphin research facilities, as well as from my personal experiences and
observations as a dolphin VIP Tour Guide and Educator.
I have made every attempt to support the information presented in this site with video and still
photographic images. On a regular basis I plan to produce more of these images and will continue to update the site with these
as well as with any new and scientifically verified information which becomes available.