The mystery of dinosaurs’ giant horns may finally be solved — and it’s about love, not war

This is the restoration of the head of Nasutoceratops

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This is the restoration of the head of Nasutoceratops
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Andrey Atuchin

  • Dinosaurs in the ceratopsian family, like Triceratops, had massive bony frills and fearsome horns on top of their heads.
  • Over time, researchers have speculated that these could have served various purposes, including defense against predators, temperature regulation, and helping to prevent mating between different species.
  • But a new study argues the primary function of these cumbersome features was probably showing off for potential mates.

For decades, researchers have tried to figure out why dinosaurs had such enormous bony frills and fearsome spikes on their heads.

They speculated that dinosaurs like the Triceratops – members of the ceratopsian or horned dinosaur family – had these distinctive traits for self-defense, or to ensure they didn’t mate with a dinosaur from another species, among other possibilities.

But according to new research, the likeliest explanation is simpler and more universal: sexual selection. While the horns might look violent, their main purpose seems to have been for picking up mates.

A study newly published in the journal Proceedings of the Royal Society B explains that dinosaurs developed these burdensome traits as ways of showing off to potential partners – the same way modern animals such as peacocks do.

“This resolves a long-standing and hitherto untested hypothesis concerning the origin and function of ornamental traits in ceratopsian dinosaurs,” Knapp said. “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.”

Understanding how the development of these traits can drive species change is important for understanding Earth’s history, and also for investigating how modern creatures may evolve in a world where there’s intense pressure to survive.

This is the Chasmosaurus skeleton in the Royal Tyrrell Museum of Paleontology.

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This is the Chasmosaurus skeleton in the Royal Tyrrell Museum of Paleontology.
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Royal Tyrrell Museum of Paleontology

Ruling out other explanations

There are more than 70 known species of ceratopsian dinosaurs, which the study explains have “exaggerated and often elaborate horns and frills, which vary considerably between species.”

Many reasons for these features have been debated over time, but some seemingly likely options – including predator defense and temperature regulation – were ruled out by previous research, according to the new study.

One lingering explanation was that ceratopsian dinosaurs used these features to differentiate between species. Animals that mate with related but distinct species can produce offspring that tends to be sterile (like mules that come from horses and donkeys). That’s obviously not a good evolutionary strategy, so paleontologists theorized that dinosaurs might use frills and horns as cues that something was or wasn’t right.

To test that theory, the authors of the recent study analyzed 350 different traits from 46 ceratopsian species. If species differentiation was a major factor, species that lived in close proximity should have evolved physical features to distinguish themselves.

But the team found that this wasn’t the case in the fossil record, which helps rule out that explanation. Plus, as we see in present-day animals, prominent differences aren’t usually needed for a creature to know whether another animal is a member of its own species.

This is the Protoceratops in the Horniman Museum, London.

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This is the Protoceratops in the Horniman Museum, London.
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Horniman Museum, London

Showing off

If the horns weren’t for fighting or avoiding sterile offspring, the likeliest explanation is that these traits were mostly about impressing potential mates.

The evolutionary record shows that these features evolved relatively quickly, which often happens because of a sexual drive.

None of this means that horns and frills couldn’t have been simultaneously used for another purpose as well – it’s possible that some dinosaurs occasionally used them to fend off or intimidate predators. But the primary role of these huge and cumbersome traits was most likely ornamental.

That’s remarkable when you consider that these features weren’t easy to live with or maintain – dinosaurs would have used up a lot of energy to carry that additional weight. But good mates, it seems, were worth the extra effort.

“Modern computer models have suggested that sexual selection can promote rapid speciation, adaptation, and extinction,” Andrew Knapp, lead study author and a researcher at Queen Mary University of London, said in a statement. “In our world of increasing pressure on the natural world, these predictions may have important consequences for conservation and the fate of living things everywhere.”