National Geographic : 2007 Dec
S TYRACO SA UR US X-FACTOR Massive hornedfrill WHEN 75 million years ago WHERE North America Like an armor-laden knight, Styracosauruswould have cut an imposing figure on the forested river plains in what is now Alberta, Canada. Multiple individuals of these rhino-size herbivores have been identified in the same bone beds, suggesting they traveled in herds. Horned dinosaurs are a well-understood group, says Hans-Dieter Sues, and since Styracosauruslived near the end of this lineage, we can trace the evolutionary paths that led to it. "Its ancestors began with a little bump over their nose and then developed a little bit of a frill at the back of the skull," says Sues, "but Styracosaurustakes these traits to the top." The bump on the nose in ancestral species evolved into an enormous spike that would have given Styraco saurusa potent weapon to fight off predators and fend off rivals. Meanwhile, the skull frill enlarged and added a profusion of horns, which probably let other styraco saurs identify it from a distance. Some scientists have suggested blood pumped into the skin cover ing the frill could have caused it to change color, possibly to attract mates or to scare enemies. "These extreme traits just didn't suddenly appear," says Sues. "There were compelling reasons why they were selected and pushed down the evolutionary line." D 56 NATIONAL GEOGRAPHIC DECEMBER 2007 t Troodon or False? How much did you learn in school about dino saurs that was all wrong? Take our quiz at ngm.com and find out.