For many people, thoughts of Triceratops conjure up a massive dino sporting sweeping horns that can drive deep into the belly of its mortal enemy, Tyrannosaurus. But scientists have no real evidence the two Cretaceous beasts ever tangled. And as Mary Halton at the BBC reports, a new study adds to the evidence that the often elaborate frills and horns of Triceratops and other ceratopsians, or horned dinosaurs, were all about looking good, not preparing them for dinosaur death matches
Over the years, paleontologists have struggled to understand why horned dinos developed such elaborate horns and frills. While common sense suggests that Triceratops' sharp horns were defensive, it doesn’t explain the ornamentation of recently discovered species like Regaliceratops peterhewsi, the “Hellboy Dinosaur” or Machairoceratops cronusi the “Bent Sword Face” dinosaur. And the number of these spike-faced creatures known to exist is climbing. In fact, the number of known horned dinosaurs that roamed Asia and North America has tripled over the last 20 years from just 23 identified in 1996.
The growing sample size of these dinos means researchers now have enough information to start answering big evolutionary questions, like why all these weird permutations of horns and plates developed. In a new study published in the journal Proceedings of the Royal Society B, researchers did just that, examining 350 traits of 46 ceratopsian species that evolved over a 15 million year time span.
Kevin Loria at Business Insider explains that if the horns and frills weren’t for fighting—a function ruled out in previous studies—another possibility is that the horns diverged to help dinos distinguish one species from another. These differences could have prevented similar-looking dinos of different species from accidentally mating with the wrong horny critter. If that’s the case, then species that lived in close proximity to each other would have evolved at different rates than species that lived in isolation.
But the analysis suggests that wasn’t the case. In fact, according to a press release, these ornaments generally evolved much faster than other traits for all the creatures.
It's pretty energy intensive to grow and carry around all the fancy head gear, so what best explains the fast, costly rise of these horns and frills? Good old sexual selection. “Individuals are advertising their quality or genetic make-up,” lead author of the study, Andrew Knapp of Queen Mary University, London, tells Halton. “We see that in peacocks too, with their tail feathers.”
That doesn’t mean the sexy masks had just one purpose. “Some of these ornaments were also likely used at times for defense against predators or, to some extent, for recognition of members of different species,” paleobiologist Darla Zelenitsky of the University of Calgary, not involved in the study, tells Halton. “But these were apparently not the primary driver in their evolution.”
Knapp says he hopes to do more work to confirm whether or not sexual selection is the main driver of the horns. "All the basic (evolutionary) models predict these changes as a consequence of sexual selection,” he tells the AFP, “extremes are selected and those traits tend to be passed on [to offspring].”
But things are a little different when it comes to horned dinosaurs. In many animals, the males usually develop crazy dances, distinctive colors, or impressive horns to attract females. But in ceratopsians, both sexes grew the elaborate facial coat racks, suggesting something unique happened within the group of dinosaurs.
This is not the first time paleontologists have crushed our dreams of a massive dino fight club. As Brian Switek reported for Smithsonian.com in 2016, researchers came to a similar conclusion about the tank-like armor and club-like tails of ankylosaur dinosaurs. There is almost no evidence that they used their tails for battle. It’s more likely the hardware was also used to show off genetic fitness, much like massive modern elephants do with their tusks.
But don’t worry, we’ll always have T. Rex to fill our dinosaur bloodlust.