Many dinosaurs had striking facial features, like aggressive horns and snazzy frills, which were thought to help them recognize other members of their clan. However, it turns out these attributes might actually be the dinosaur version of dressing to impress, helping to entice the opposite sex.

Last year, researchers from Queen Mary University of London concluded that a dinosaur called Protoceratops likely used its ornamental features in sexual displays, a first in the world of palaeontology. Now the team has investigated further, this time looking at the geographical distributions and physical attributes of 46 different species of ceratopsians, otherwise known as the horned dinosaurs.

They found that dinosaurs within this group, which includes species such as Triceratops, had striking facial ornamentation like horns and frills regardless of whether they lived together in groups or wandered alone. Although these features might have helped dinosaurs to recognize others of the same species, something that prevents crossbreeding and production of infertile offspring, it wasn’t the primary driving force behind their evolution.

What’s more, the researchers found that these attributes seemed to evolve unusually fast, despite being energetically expensive to grow and maintain. This all points towards sexual selection as the culprit behind their evolution, not species recognition. The findings are published in Proceedings of the Royal Society B.

Unlike normal natural selection, which involves those with traits beneficial for survival being more likely to survive, reproduce, and pass on their genes, sexual selection involves sex. Even Darwin was puzzled by the fact that many species have evolved weird, unnecessarily elaborate characteristics that are more likely to hinder them than help them survive, like the peacock’s elaborate tail. So, to make sense of it, Darwin came up with sexual selection. In other words, it’s survival of the sexiest, not survival of the fittest.

Although the peacock’s tail is costly to grow and maintain, males with the biggest, brightest tails are more likely to attract admiring females, mate, and pass on their elaborate tail genes to the next generation. Meanwhile, females reinforce this by choosing males with the most eccentric tails. The same likely occurred with the large horns and fancy frills of the dinosaurs long ago.

"This resolves a long-standing and hitherto untested hypothesis concerning the origin and function of ornamental traits in ceratopsian dinosaurs,” explained lead author Andrew Knapp in a statement. “Many general discussions of ceratopsian ornaments in museum signage and popular literature often include examples of what they might have been for, but these tend to be rather speculative.

"If sexual selection is indeed the driver of ornament evolution in ceratopsians, as we are increasingly confident it is, demonstrating it through different lines of evidence can provide a crucial window into tracing its effects over potentially huge timescales."