Pictured: A sexy beast. Photo courtesy EvaK via CC
You know. It.
Sexual practices don't really leave much of an imprint in the fossil record. And dinosaurs, themselves, are not, shall we say, the most nubile-looking creatures. According to paleo-blogger Brian Switek, you aren't alone in your confusion. He says scientists have been pondering dino-sex for more than 100 years. (Like you do.) In fact, until recently, paleontologists weren't even totally clear which dinosaurs were girls and which were boys.
And, once that mystery was solved, there were still a lot of other obvious questions. Such as: How did pointy, heavily-armored Stegosaurs get amorous?
Soft-tissue preservation is very rare, and no one has yet discovered an exquisitely preserved dinosaur with its reproductive organs intact. In terms of basic mechanics, the best way to study dinosaur sex is to look at the animals' closest living relatives. Dinosaurs shared a common ancestor with alligators and crocodiles more than 250 million years ago, and modern birds are the living descendants of dinosaurs akin to Velociraptor. Therefore we can surmise that anatomical structures present in both birds and crocodylians were present in dinosaurs, too. The reproductive organs of both groups are generally similar. Males and females have a single opening–called the cloaca–that is a dual-use organ for sex and excretion. Male birds and crocodylians have a penis that emerges from the cloaca to deliver sperm. Dinosaur sex must have followed the "Insert Tab A into Slot B" game plan carried on by their modern-day descendants and cousins.
Figuring out how Stegosaurus even could have mated is a prickly subject. Females were just as well-armored as males, and it is unlikely that males mounted the females from the back. A different technique was necessary. Perhaps they angled so that they faced belly to belly, some have guessed, or maybe, as suggested by Timothy Isles in a recent paper, males faced away from standing females and backed up (a rather tricky maneuver!). The simplest technique yet proposed is that the female lay down on her side and the male approached standing up, thereby avoiding all those plates and spikes.
You've really got to read this entire article. Out loud. To someone you love. If they're the kind of lover who wants to know about prehistoric mating rituals, the dino-sex theories of Victorian paleontologists, or how to sex a fossil, they'll thank you. (And if they aren't that kind of lover, well. Maybe it's time to re-think the relationship.)