Dinosaurs’ Violent Mating Habits Are Helping Us Identify Their Genders

If you’ve ever wondered how dinosaurs had sex, don’t think of yourself as a filthy pervert. Just think of yourself as an esteemed researcher pondering one of paleontology’s most vexing questions. It’s something actual paleontologists have been wondering for years, particularly while looking over the remains of duckbilled dinosaurs known as hadrosaurs.

Publishing their findings in iScience, researchers might finally have the answer, and it seems painful. But that answer helps us better understand which bones belong to males and which to females.

A new study led by Professor Eileen Murphy from Queen’s University Belfast found that the top vertebrae of hadrosaur tails, specifically the part closest to their cloaca, frequently show signs of healed fractures. The pattern was the same across hundreds of fossils from Eurasia and North America, suggesting a shared behavior rather than injury or an attack.

The Sex Lives of Dinosaurs Are Helping Us Tell Males From Females

No bite marks meant a predator hadn’t attacked it, and the breaks weren’t in spots that would be consistent with combat injuries as it swung its tail around to fend off foes. That left only one explanation: sex, and some particularly violent sex at that, wherein males crushed females’ tails during mounting.

Computer models confirmed that the forces required to break those bones lined up well with the physics of dinosaur sex. Just imagine several tons of prehistoric sexual enthusiasm crashing down on you at a slightly off angle. Something is going to get broken.

This rough sex wouldn’t permanently injure the female. The fractures showed signs of healing, indicating the females survived and likely continued reproducing. The broken bones were just an occupational hazard, and the injuries female hadrosaurs had to endure in the name of procreation.

As one of the study’s authors, Professor Gareth Arnott, notes, many modern species, such as sea lions and some turtles, also bang violently. These are fairly clumsy creatures, after all, trying to perform an act that requires a little more dexterity and mobility than they’re probably capable of.

But they manage it, with some painful side effects. As the study’s first author, Filippo Bertozzo, put it, this opens “the first door on sexual behavior of dinosaurs.”