Size matters: Dinosaurs grew horns to be 'sexy,' researchers say

Horned dinosaurs may have been more attracted to mates who had a nice, sturdy set of horns, spikes and frills, a new study has found.

"That could be because a bigger horn is a fundamentally a better show of quality: I am healthy, therefore I can grow lots of bone and carry it around without being eaten," paleontologist Dave Hone told As It Happens host Carol Off. 

"Or it could just be: Horns are actually quite sexy. I'm into horns and that one's got a bigger horn."

Hone is the co-author of the Queen Mary University of London study, which was published Wednesday in the Proceedings of the Royal Society B journal. 

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The researchers were testing the popular hypothesis that ceratopsians, or horned dinosaurs, grew their ornaments to distinguish between different species and guard against cross-species breeding.

But when they examined the horns, frills and spikes of 46 ceratopsian species, they found no difference between species that lived together or those that lived separately.

Instead, the researchers believe it's likely that horns evolved because dinosaurs were more likely to hook up with a big-horned mates.

"We think that, really, it's mostly a big kind of display feature, so just as peacocks have their big showy feathers and lions have the big mane and deer have big antlers," Hone said.

"It's some kind of big advertising feature for these animals to show off."

Mutual attraction 

But unlike peacocks, it's not just a cocky display of male prowess. 

Both sexes of ceratopsians have horns and likely used them to attract each other, Hone said.

That could mean males and females shared parenting duties, he said. 

"That comes about because both of them are investing," he said. 

"When you look at something like a peacock, the male is basically providing genetic material and basically nothing else."

By comparison, he said both male and female parrots have bright plumage, and they care for their young together. 

"It's in his interest to make sure that he has a bright and healthy and attractive partner, just as much as it's in the female's interest to make sure she has a bright and healthy and attractive male," Hone said. 

Locking horns in battle

Horns are also useful for self-defence, Hone said, noting there's evidence of Triceratops fighting Tyrannosaurus rex.

"That doesn't mean that it's mostly what those horns are evolved for," he said. "That could be just a byproduct, rather than the primary evolution driver."

In fact, there doesn't have to be one single reason, he said. 

Deer use their antlers to attract mates, fend off predators and fight each other, Hone noted. Elephants use their tusks in battle, but also to access water. 

"It's actually quite complicated," he said.

Written by Sheena Goodyear. Interview produced by Sarah Jackson.