For years, paleontologists have theorized that many of the world's largest dinosaurs sported head ornaments (think horns, knobs, and crests) as a means of intimidation and defense, and that these giants evolved to be so big because size helped them be more effective killers. But now new research published in the journal Nature Communications suggests that these ornaments were in fact a "signaling structure" that attracted prospective mates. In other words, it could be about sex instead of brutality—and head ornaments aren't merely a byproduct of being large but in fact a reason for it, the Smithsonian reports. "We were surprised to find such a strong relationship between ornaments and huge body size," lead author Terry Gates says in a press release from North Carolina State University.
"Something about their world clearly favored bling and big bods," he adds. Studying 111 skulls of theropods—which Live Science reports were mostly carnivorous and bipedal dinosaurs, T. rex and Albertosaurus among them—researchers found that 20 of the 22 biggest had bony structures protruding from their skulls, while only one of the dinosaurs smaller than 80 pounds did. Just as intriguing, they found that those with head ornaments increased in size an astonishing 20 times faster, amounting to an additional several hundred pounds every 4 million to 6 million years. "Once you get crests, your body size just shoots up super fast," the lead author says. (Here's why some dinosaurs appear to have sported lips.)