How did dinosaurs have sex? – Slate Magazine
From behind, probably. Paleontologists know very little about how dinosaurs mated, because soft tissue rarely appears in fossils. (They figured out how to determine dinosaur gender only a few years ago: Females had a special calcium reservoir to help with eggshell formation.) It is highly probable that dinosaurs had a cloaca—as do most birds and reptiles—which is a single opening for urination, defecation, and reproduction. If that’s the case, we might speculate that the male and female would have aligned their cloacae such that the male’s penis could emerge to penetrate the female cloaca. (It’s also possible that dinosaurs had no penises, and, like some birds, reproduced by squirting semen from one cloaca at another.) Modern ornithologists and herpetologists call this a “cloacal kiss .” Beyond that, it’s all conjecture. Paleontologists can only guess about mating positions, duration, and behavior. The majority view seems to be that large males like the Mamenchisaurus—a 60-foot-long behemoth featured in the new exhibition—probably mounted from behind, like modern giraffes and elephants.
Unfortunately, we know almost nothing about the size of other, more intimate dinosaur parts. The ratio of penis length to body size varies so widely among dinosaur relatives that it’s hard to make a solid guess about a dinosaur’s endowment. Some ducks, for example, are just a couple of feet long, but have 7-inch penises. On the other hand, crocodiles that grow to 15 feet sport just a 4-inch organ. If you applied those ratios to the 40-foot-long body of a Tyrannosaurus rex, you’d get a penis of anywhere between 10 inches and 12 feet.
Paleontologists have spent a lot of time musing about dinosaur sex positions, and they can’t agree on very much. For example, even though sex for large, long-necked dinosaurs probably looked something like giraffe mating, there’s a dispute as to what the male did with its head. Some researchers believe he couldn’t have maintained adequate blood supply to the brain with it so high off the ground, so he must have gotten into some kind of high-pelvis, low-neck position. Others believe he could have held his head up high and proud during his few moments of glory.