The Obligatory Valentine's Story

The "news" is abuzz, according to the yearly ritual, with stories about love and romance. The New York Times, for example, is currently running a story on romances between vegetarians and meat-eaters (as well as other conflicting dietary modes), new research on how the couples' "date night" may be a waste of time if it, too, becomes routine, and a piece on physical mimicry and the psychology of affinity (which is way more interesting than that description makes it sound -- it means you like people who act like you do). Each of these are interesting, quality Valentine's-Week stories, and I recommend them all!

But my favorite Valentine's Week story will be this one, about T-Rex penises, by Olivia Judson. Judson is new to the Times, and is quickly becoming one of my favorite columnists anywhere.

...if you tell me a fact, such as the average size difference between males and females in a species, or the proportion of a male’s body taken up by his testes, I can tell you what the mating system is likely to be. For example, where males are much bigger than females, fighting between males has been important — which often means that the biggest males maintain a harem. If testes are relatively large, females probably have sex with several males in the course of a single breeding episode.

These forces are so reliable that, if only we could determine the sex of dinosaur fossils, we could begin to infer their mating habits.


Which brings me to my tyrannical fantasy. I want to take a journey 68 million years back in time to see a Tyrannosaurus rex couple mating. What was it like? Did they trumpet and bellow and stamp their feet? Did they thrash their enormous tails? Did he bite her neck in rapture and exude a musky scent? Somehow, I imagine that when two T. rex got it on, the earth shook for miles around.

And if I could only take this journey, I could answer a question that sometimes bothers me. Did T. rex have a penis? Did he even, as lizards do, have two?

I ask the question not out of prurience, but because it’s a matter of scientific interest. There are a couple of reasons why. First, the penis is another important indicator of the mating system. In species where females usually mate with a single male during a breeding episode, penises tend to be small and uninteresting. In those where females mate with several males (whether by choice or by force), penises are typically larger, and come with fancy decorations such as grooves, nobbles, and spikes. Second, the question of the dinosaur penis provides an exercise in evolutionary inference.

The reason we don’t know whether T. rex had one is that the organ is generally too soft to leave a fossil trace. (There’s an exception to this: some mammals have a bone in their penis, the os penis or baculum. This can fossilize. Humans are unusual among primates in not having one; in case you’re wondering, it’s not clear whether the bone plays a role in maintaining erections.)

Moreover, whether a male has a penis at all varies from one group to the next. Male salamanders, for instance, don’t: they deposit sperm on the ground and the female collects it. Among birds, penises are rare: ostriches, emus, ducks, geese and swans are among the few. The rest just have a cloaca — an all-purpose opening also used for urination, defecation and, in the female, laying eggs. To copulate, two birds bring their cloacae together in what’s called a cloacal kiss.

So what can we say about dinosaurs? My guess is that the males had members — but it’s an educated guess. It’s based on an analysis of dinosaur relations.

Read Judson as she reasons out the mystery of the T-Rex penis, by clicking here.

Happy VD!

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