Mating injuries may give us a new way to identify dinosaur genders

Paleontologists have long wrestled with the challenge of identifying the genera of dinosaurs from the fossils they leave behind. Once soft tissues such as the reproductive organs are removed, it is almost impossible to distinguish a male from a female and this has fueled much debate. But there may be an easier way to solve the mystery, at least for one group of dinosaurs.

A new study published in the journal isciment suggests that traumatic injuries during mating may be the key to determining dinosaur sex.

Analyzing the evidence

The hadrosaurids, commonly known as the duck-billed dinosaurs because of their broad, flat snouts, are a group of dinosaurs that lived during the Cretaceous period. Many fossils show evidence of healing dissolution with long, bony spikes in the middle of their tails. But what is the reason for these intervals?

Over the years, the debates have ranged from accidental trampling to intraspecific fighting. To solve this, researchers led by Dr Filippo Bertuzzo of the Royal Belgian Institute of Natural Sciences set out to find an answer, and in doing so, may have discovered a way to identify female individuals.

The research team analyzed 551 neural spines from hadrosaur fossils from museum collections in North America, Europe and Asia, spanning different time periods. This confirmed that the pattern of repetitive injury was consistent across species and locations. They then created 3D models of tail bones from Edmontosaurus dinosaurs (one of the most completely preserved hadrosaurids) and used computer simulations to determine what kinds of forces might have caused the breaks found in the fossil.

Rejecting the usual suspects

The only force that matched the injuries was a diagonal weight pressing on the top of the tail at an angle between 30 and 60 degrees. The team ruled out other causes, such as trampling and fighting, because they would cause different types of injuries. For example, if there was a predictable cause, you would see teeth marks on the bones, but they are not there.

The scientists concluded that symmetry was the most likely cause of injury for several reasons. The computer-generated diagonal force corresponds to the weight of a growing male pressing on a female’s tail at the point where the cloaca is projected. Additionally, almost all of the fossils were from adult specimens, indicating that trauma was caused by adult-like behaviors, such as mating.

“These possible mating injuries may represent the first indirect evidence of sexual behavior in a non-avian dinosaur, and a new approach to recognizing female individuals,” the researchers commented.

If the work is correct, science may have a new way to identify female dinosaurs among many other species.

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