Dinosaurs are not the only animals with unusual features--think of a porcupine's quills or a peacock's tail. Indeed, many creatures have bizarre structures like horns, trunks, tusks, shells and more. Dinosaurs didn't stop with horns either, but had crests, spikes, domes, armor or plates.
Consider the duck-billed dinosaurs, or hadrosaurs. Famous for their distinctive beaks, some duckbills also had another interesting feature: large, hollow, sweeping crests on the tops of their skulls. The crests were covered in skin that may have been brightly colored. Some scientists think hadrosaur crests could have been used as part of mating rituals, much as peacocks use their tails. Duckbills with the most spectacular crests might have been the most attractive to members of the opposite sex.