Pachycephalosaurus is a genus of herbivorous dinosaur that lived during the Late Cretaceous period around 70 million years ago, in what is now North America. Its name means “thick-headed lizard,” referring to the thick dome-shaped bone on its head that is its most distinctive feature. This bone was over 10 inches thick in some specimens and is believed to have been used for head-butting contests between males during mating season.

Pachycephalosaurus grew up to 20 feet in length, weighed around 450-990 pounds, and had a small body with powerful hind legs that allowed it to run quickly. Despite its name and appearance, Pachycephalosaurus was not a dinosaur that could defend itself against predators, and instead likely relied on speed and agility to avoid danger. The teeth of Pachycephalosaurus were leaf-shaped and suited for eating tough vegetation, such as ferns and horsetails.

The bones of Pachycephalosaurus have been found in large numbers in North America, suggesting that it was once a common dinosaur in its environment. However, much is still unknown about the lifestyle and behavior of this fascinating and enigmatic dinosaur.