One day, Reddit user kwhishe was just casually chatting with friends, shooting the shit. Suddenly, the conversation veered towards dinosaur balls.

“The other day, I was in a group of people when someone was making a gesture with their hands saying that someone else had huge balls, using each hand to hold one ball, so my friend exclaimed that those would look more like dinosaur balls (we had just watched Jurassic World). “Then we got curious about the actual size of dinosaur balls, and a quick search showed that scientists can’t be sure if dinosaurs actually had testicles in the sense that we know them now, if [at] all. So, I just wanted more information on why we don’t know positively if dinosaurs had testicles, and if they did have balls, how large would they be?”

This question is nuts! But truly, I was elated. Dinosaur peen is a topic that’s come up a lot for whatever reason in drunken conversation (which may say more about the company I keep more than anything), but dinosaur testicles is a subject that’s sorely ignored.

I guess most people just assume T. rex had big balls dangling about, which couldn’t be more further from the truth.

I contacted Matt Borths, host of the amazing and fascinating Past Time podcast. As an Ohio University paleontologist, the ball was really in his court to investigate this further.

Immediately, Matt told me that dinosaurs did have testicles! How big they were was a matter of debate. And, really, that’s the question that’s on everyone’s mind.

Borths says that all sexually reproducing animals have testicles, as in, a storage place for sperm. Before you get too excited, you mustn’t confuse this for balls, however.

Mammals are unique in that aspect. As I’m sure you’re aware, males, curiously and weirdly, have external testicles hanging in between their legs. This makes no sense evolutionary-wise, considering anyone who has been kicked in the balls knows just how vulnerable and defenseless this mechanism is. But we’ll get to that later.

Borths explains:

“If you go to the zoo and check between the legs of all the animals you see, you’ll be hard pressed to find a critter with balls that isn’t a mammal. Because there aren’t any. Mammals are the only animals that have taken the apparently idiotic evolutionary step to let half the genetic diversity of future generations hang out in the wind.”

Here’s the thing: Nobody knows why mammals possess external balls. There are a bunch of theories dangling about, like temperature regulation (some say sperm production is best a few degrees cooler than your body temperature).

In truth, mammal testes are really one of science’s greatest mysteries. Right up there with the origin of the universe. Seriously.

On the other hand, reptiles, amphibians, and birds have internal testicles. Some mammals do, too.

“Whales, hedgehogs, and rhinos have independently taken the sensible evolutionary step to tuck their testes back inside the abdomen,” explains Borths.

So based on this information, we can conclude that dinos possessed internal testes. But how big were they? Who knows?

Paleontologists have never actually found fossilized T. rex testes. Since testicles are essentially soft tissue, they don’t fossilize very well.

“In fact, for most dinosaurs, we can’t say if we’re dealing with a male or female individual,” he shares. Only a handful of definite female dinosaurs have ever been found.

Since we don’t have any fossilized records of dino gonads, we have to look towards their modern-day descendants: birds and their closest living relatives: crocodiles.

In birds, there is a lot of variation in testicle size based on the species. And, like crocodiles, their testicles actually change in size during breeding season.

“Big dinosaurs probably had pretty big testes because they were big, but there would have been a lot of variation,” Borths says.

It’s really hard to say. Body size doesn’t necessarily equate to ball size in mammals all the time.

“Even just within apes, things get pretty crazy with some researchers connecting social behavior to ball size,” Borths explains.

He went on to say a sentence that, while scientific, just made me laugh at the absurdity of our conversation: “Gorillas have pretty tiny balls compared to their body size.”

Scientists think this may be because one gorilla has access to a harem of females. Chimps, which are much smaller, have huge testicles which might be advantageous in their environment where multiple males and females compete for sex with each other. Humans are somewhere in between.

“Same with dinosaurs. Depending on the breeding season and the composition of groups, and the strategies used by males and females to get access to each other,” Borths says, “there was probably a lot of variation in testicle size between species and even within an individual depending on the time of year.”

There you have it! Nobody really knows about the inner workings of dinosaurs’ delicate bits, but we can make some ballsy guesses regardless.