Pachycephalosaurus, the "Thick-Headed Lizard," is a wildly popular dinosaur due to the theory that it used its iconic dome-shaped head to ram into each other like bighorn sheep. However, there is significant debate in the scientific community over head-butting's feasibility. Some paleontologists believe that the Pachycephalosuaurs' skeletons were too weak for it, but others argue that the amount of infections on their domes show that they did engage in this form of combat. But at four and a half meters long, one and a half tall, with a twenty-five centimeter thick skull, Pachycephalosaurus could still pack a punch no matter how they fought. Males likely had thicker skulls than females, either for display or for battling for mates. Pachycephalosaurus' western United States home was a mild to subtropical coastal plain at the end of the Cretaceous Period. Their small teeth were probably used to nibble on soft plant matter as they roamed the countryside. They lived there alongside fan-favorite herbivores like Ankylosaurus and Triceratops and also with the fearsome killer Tyrannosaurus. The presence of two smaller, less developed pachycephalosaurids, Dracorex and Stygimoloch, leads paleontologists to think that these species may actually represent growth stages of Pachycephalosaurus instead of separate taxa.