Paleontologists have found the first convincing evidence of sexual dimorphism in Stegosaurus mjosi, a species of dinosaur. Sexual dimorphism means the anatomical differences between males and females of the same species. According to a study published in the journal PLOS ONE, the bony plates that lined the Stegosaurus‘s neck, back and tail might have differed between males and females.

Stegosaurus' Bony Plates Help Determine Sex In Dinos

Wide plates were 45% larger than tall ones

Evan Saitta of the University of Bristol and lead author of the study, studied Stegosaurus fossils recovered from Montana. The Judith River Dinosaur Institute (JRDI) in Montana is a dinosaur graveyard that has a lot of Stegosaurus fossils from the same time period. While analyzing 150-million-year old remains of the dinosaur, Saitta found that some individuals had tall plates while others had wide plates.

He took measurements and CT scans of 10 bony plates from the Montana graveyard, and also included 30 plates of Stegosaurus from earlier research, according to Live Science. He found that the wide plates were 45% larger than the tall ones in surface area. Then he explored other possible causes of the differences in plates. The dinosaurs in Montana graveyard were buried together, suggesting that they lived together.

Wide plates belonged to male Stegosaurus?

He checked whether it was merely variation within individuals. But that was not the case because there were only two types of plates, wide and tall. There were no intermediates. It’s quite difficult to determine the sex of dinosaurs. Saitta argued that males probably had wide plates and females had tall plates. He said that male animals spent more energy in their ornamentation. The wider plates were larger, so they would have required more energy to grow.

Females might have used tall plates as a prickly deterrent against potential predators. Andrew Farke of the Raymond M. Alf Museum of Paleontology said more research was needed before bony plates can be declared the predictors of sexual dimorphism in dinos. Saitta believes that other dinosaur species also exhibited sexual dimorphism.