How Did Dinosaurs Have Sex?

Dino-style.

By Brian Palmer

Illustration by Alex Eben Meyer. Click image to expand.The American Museum of Natural History in New York will unveil an exhibition of the world’s largest dinosaurs this Saturday. Some visitors may wonder how the creatures could ever eat enough to sustain their size, but the Explainer’s mind is in the Jurassic gutter. How did those monsters manage to have sex?

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.

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