Did Dinosaurs Have Dicks?
By: Sam Westreich
Tags: Biology, Science, Dinosaurs, Paleontology, Sex

Recently, in an effort to not spend literally all of our time social distancing inside our house, my wife and I took a trip to the Oakland Zoo for some evening entertainment — a Glowfari.

The zoo is now running an evening program, open to the public with a reservation purchased in advance, where visitors can wander around the zoo grounds. Instead of seeing animals, however — who generally don’t glow and aren’t that interesting to look at after dark — the zoo has dozens of large, lit up, animated statues of various animals.

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.

Namely, did male dinosaurs have penises?

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.

But it’s a scientific question and I want answers — let’s do some research and try to figure out how dinosaurs had sex!

Sadly, Dongs Don’t Age Well

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).

This is one of the reasons why we still aren’t sure whether or not dinosaurs were covered in feathers. While the bones of dinosaurs were hard enough to leave impressions, and thus later be replaced by stone so that we could see fossils, softer tissue like skin, feathers, organs — and penises — aren’t preserved. They’re rotted away before they can be replaced with stone.

“Yes, yes, very scary. But are you a scary boy, or a scary girl?” Photo by Fausto García on Unsplash

In fact, a huge challenge with individual dinosaur fossils is even determining whether they were male or female! We’ve only recently discovered the presence of a bone in females that indicates whether they were pregnant when they died; this serves as a method for determining sex.

(That bone, by the way? It was a way to store calcium for future offspring, a trick that’s used by birds today.)

This means that we don’t have any fossilized dinosaur penises that we can point at as conclusive evidence.

In fact, looking at the descendants of dinosaurs — the birds that flap around, steal our bread crusts, and even become our child’s favorite meal of chicken nuggets — they may not have existed at all.

Birds Being Busy By Boinking

It’s weird to admit, but I’ve never really looked for the penis on a bird.

I suppose that part of me considered that it just wouldn’t be easy to see; they’ve got feathers and such, that could cover it up. But as it turns out, it’s not my bad eyesight or proper Victorian habits; the vast majority, more than ninety percent, of birds don’t have penises.

Then how do they mate?

Birds, like many other animals, have a cloaca — a single hole that serves as the exit point for all waste from their body. This is also the exit point for all reproductive components, including sperm or eggs. (Humans don’t have a cloaca, since we have separate openings for liquid waste and solid waste — and in the case of women, another opening for reproduction.)

Most birds, without penises, simply eject their sperm out through their cloaca. In order to ensure that this transfers successfully to the female, they will press their cloacas together in a “cloacal kiss”.

But this isn’t an answer to our dino question, and even though most birds have lost their penises, not all of them are set up in such a fashion. Some birds — notably ducks, but also ostriches and some others — still have penises.

It’s a similar situation when we look at the reptile world. Most reptiles simply have a cloaca, but crocodilians also still have their penises.

Therefore, it’s a possibility that dinosaurs didn’t have penises, and instead simply squirted sperm out their cloacas at each other.

Does Size Matter?

On the other hand, many of the birds and reptiles that still have their penises are from older lineages, further back on the evolutionary tree. This indicates that dinosaurs may have had penises, after all.

And when we look at birds, it’s tough to say just how much heat a dinosaur might have been packing. Most of the birds that still retain a penis have small, almost vestigial penises — but some, such as ducks, are extremely well endowed.

The average duck penis is about seven inches, compared to their two feet of height. For a human, that’s equivalent to more than a foot and a half on the average (5'6") male.

A crocodile, on the other hand, only has an average penis length of about 4 inches, compared to its fifteen feet of body length.

So dinosaurs may have been well endowed, or staying small, sleek, and trim. Unfortunately, without more evidence (or a working time machine), it’s going to be difficult to determine more details.

One challenge for dinosaurs that may have predicated the need for a penis is the mechanics of sex, when dealing with very large bodies. Most paleontologists assume that dinosaurs performed mating in a similar manner to large animals today, with the male often mounting the female from behind. Analysis of large plant-eating sauropod fossils show that, despite their massive weight, they were likely able to support the short-term weight of their mating partner.

For other dinosaurs, however, such as the Stegosaurus, mating may have been performed while one animal lay down, to avoid spikes and other defenses.