Scientists Clash Over Stegosaurus Sexing

A new paper is causing controversy with claims that dinosaurs’ sex can be determined by their bones

Craig Brown/Stocktrek Images/Corbis

It’s a claim that could change the way we think about dinosaurs. But a new paper that argues scientists could tell the difference between male and female Stegosaurus by the shape of their plates is coming under fire from paleontologists.

Behind the controversy is a student named Evan Saitta. While attending high school, he took a trip to Montana’s Judith River Dinosaur Institute, where he became fascinated by the prehistoric creature’s plates—the characteristic bony bits that rise up along the spine of the Stegosaurus's back. He tells LiveScience’s Laura Geggel that the quarry where the fossils were found contains remains of multiple different Stegosaurus from the same time period, which sparked his interest in comparing the different animals' armor.

With the help of CT scans and measurements, Saitta began to study the fossils and compare his results to plates and replicas contained in other collections. In his study, he identified two distinct forms of plate: tall and wide. Wide plates had surface areas of up to 45 percent higher than their tall counterparts.

Saitta then ruled out the possibility that the different dinosaurs were different species, or perhaps still growing. Once he was convinced that neither of those things could explain the differences, Saitta floated an intriguing idea: What if plates were instead evidence of sexual dimorphism, or difference between sexes? “As males typically invest more in their ornamentation, the larger, wide plates likely came from males,” said Saitta. “These broad plates would have provided a great display surface to attract mates. The tall plates might have functioned as prickly predator deterrents in females.”

But response to the paper has been decidedly frigid within the field. Nature’s Angus Chen reports that paleontologists like UC Berkeley’s Kevin Padian claim Saitta misidentified features in bone tissue that he used to rule out growth as a factor in plate size. And others have challenged Saitta’s use of reproduction plates and privately-held bones into question, citing ethical issues that prevent other paleontologists from using specimens that “are not in the public trust.” These ethical considerations are common for paleontologists, who are ethically bound to use publicly-available and legally-obtained specimens in order to conduct reproducible research.

As for Saitta, he stands by his work. “I want people to focus on the science,” he told Chen. And Michael Benton, director of the paleobiology program where Saitta is currently a student, is proud of Saitta’s accomplishment. “Evan made this discovery while he was completing his undergraduate thesis at Princeton University,” he notes in a release. “It’s very impressive when an undergraduate makes such a major scientific discovery.”

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