It is believed that dolphins may possibly engage in this type of behavior to learn about sex as well as to maintain strong social bonds for many sorts of cooperative activities. Therefore, male dolphins have both their penis and testicles packed inside their body. On mammals, testicles are usually found outside the body since sperm dies at body temperature. Dolphins compensate for the extra heat that their testicles must endure by utilizing a special feature of their circulatory system. Male dolphins are also designed to have quick erections.
Ejaculation seems to be under voluntary control.
In fact, one of DRC's dolphins has been trained to ejaculate on command. Mating must occur quickly in the wild, so this is advantageous to a male dolphin. Imagine if you were in the middle of mating and a bull shark appears. You would certainly want to be able to finish spreading your genes and get out of the area in a hurry. It is thought to be a possible evolutionary link to their land ancestors.