Pachycephalosauria is a group of herbivorous dinosaurs known for their thick, domed skulls. These dinosaurs lived during the late Cretaceous period, around 75 to 65 million years ago. They were primarily bipedal and had strong legs, which helped them move quickly. Their unique skull structure is believed to have been used for head-butting or display purposes. Members of Pachycephalosauria include well-known species like Pachycephalosaurus and Stegoceras. Fossils have been found mainly in North America, providing insights into their behavior and environment. These dinosaurs were part of a diverse ecosystem, coexisting with other species during their time.