One of our biggest challenges in understanding how dinosaurs lived, ate, and reproduced is the limited information that we have about them. We only have fossils — and fossils don’t preserve soft tissue (with a few very rare exceptions).

Blue whales are the largest creature to ever roam the earth, and they certainly have the phallus to match. Blue whale penises range between eight and ten feet, with a foot-long diameter. Each of its testes along can weigh up to 150 pounds and can ejaculate gallons of sperm in a single go. You just need to go look that one up,” says Willingham. You can see a video of the slugs in action here.

Brennan, P., Birkhead, T., Zyskowski, K., van der Waag, J., & Prum, R. (2008). Independent evolutionary reductions of the phallus in basal birds Journal of Avian Biology, 39 (5), 487-492 DOI: 10.1111/j.0908-8857.2008.04610.x Sato, T., Cheng, Y., Wu, X., Zelenitsky, D.K., Hsaiao, Y (2005). A Pair of Shelled Eggs Inside A Female Dinosaur Science, 308 (5720), 375-375 DOI: 10.1126/science.1110578 There's not a binary that is categorically one thing or the other when it comes to genitalia,” says Willingham. There is much we don’t know about dinosaur sex. From possible positions to anatomy, mysteries abound. But the subject has moved beyond silly speculation. A better understanding of dinosaur evolutionary relationships has given paleontologists a framework from which to hypothesize about different aspects of dinosaur reproduction, and those ideas have been tested by discoveries in the fossil record. Future finds and analyses will undoubtedly flesh out some of the remaining unknowns. We are only just beginning to discover some of the most intimate secrets of dinosaur lives.

This is the final installment of the dinosaur sex series. For more, please see my Smithsonian article “ Everything you wanted to know about dinosaur sex” and the previous entries in the series: It’s… not the sort of question that’s usually covered in children’s books, which is why I don’t know the answer from my childhood wealth of knowledge about most things dinosaurs. We will probably never know the full range of dinosaurian penis variation. I doubt that such diverse and disparate creatures would have had a one-size-fits-all anatomy, although I also doubt the horrifying idea— which comes up often in internet comment threads—that male dinosaurs might have had long, prehensile organs which allowed them to inseminate at a distance. No matter what their gonads looked like, though, male dinosaurs probably had to get very close to their female partners during sex. There were only a limited number of positions which would have worked for dinosaurs. Their two-headed penises resemble tiny swords, and battles can last for up to an hour as they take turns attempting to stab the other. The winner pierces the flesh of the other flatworm to deposit their sperm, something scientists refer to as “traumatic insemination.” Mating leopard slugs dangle from branches by a shared rope of their own slime with their penises hanging below. As hermaphrodites, these slugs inseminate each other during sex so, once the action starts, two penises are on display. And their penises are easily spotted: They’re electric blue and roughly the size of the slugs themselves.

Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs. Bloomington: Indiana University Press. pp. 78-81 Of course, no one expects these glowing statues to be completely anatomically correct. However, while wandering through the Land of the Lost section, an interesting question was raised about the dinosaurs. But we actually know a little more about the reproductive anatomy of female dinosaurs than male dinosaurs. Dinosaur penis anatomy is constrained by what we know about the evolutionary relationships of dinosaurs and what we are willing to imagine, but a few significant fossils have given paleontologists a general idea of the female dinosaur reproductive tract. The most fantastic of them is a pelvis of an oviraptorosaur—one of the feather-covered, beaked dinosaurs that were relatively close cousins of dinosaurs like Velociraptor—with two eggs preserved inside. Described in 2005 by Tamaki Sato and colleagues, the hips show that the female oviraptorosaur had died just before laying those eggs. This fortuitous discovery illustrated that at least some dinosaurs had a mix of bird- and crocodylian-like reproductive features.