Pachycephalosaurs were a group of herbivorous, bipedal dinosaurs that lived during the Late Cretaceous period. Commonly known as "thick-headed lizards," these dinosaurs had thick, domed skulls that were used for head-butting during fights and mating displays. While "pachycephalosaur" is the most commonly used term for these dinosaurs, there are several other synonyms that are sometimes used in scientific literature. These include "bone-headed dinosaurs," "dome-headed dinosaurs," "thick-skulled dinosaurs," and "bulb-headed dinosaurs." Regardless of the term used, pachycephalosaurs are known for their distinctive anatomical features and unique behavior patterns.