Scientists are unsure of the exact body movements involved in stegosaurus copulation because there are no modern examples available; however, they have several theories based on the dinosaurs' living descendants. Certainly the male did not mount the female like most animal species. Instead, it is possible they lay belly to belly, or the female laid down while the male stood beside her. Scientists even suggest they might have stood back-to-back.
It is a known fact that dinosaurs, including stegosaurus, laid eggs. Biologically, then, the time necessary for reproduction was minimal, although they did have to have actual physical intimacy, unlike fish. Instead, like modern birds, it is possible that a small amount of sperm deposited into the female could fertilize eggs for several weeks.
Since no preserved soft tissue or impressions of soft tissue have been located from any dinosaurs at this time, it is impossible to know how these very bony, prickly creatures reproduced. Like modern porcupines and hedgehogs, though, it is clear that they did reproduce for thousands of years. Nature always finds a way, and it is possible that the genital organs for both male and female were specially shaped to allow the process to take place without too much difficulty.