PACHYCEPHALOSAURUS

Pachycephalosaurus (say that five times fast!) was a truly unique dinosaur from the Late Cretaceous period. Its name means "thick-headed lizard," and boy, does it live up to its name! The most striking feature of Pachycephalosaurus was its incredibly thick skull dome, which could be up to 25 centimeters (10 inches) thick! Scientists used to think they used these domes to headbutt each other like bighorn sheep, maybe to show who was the boss or win a mate. However, some scientists now believe the dome might have been too fragile for that, and they might have butted flanks instead.

This bipedal herbivore roamed what is now Montana, South Dakota, and Wyoming in the USA. They were about 4.5 to 5 meters long and stood about 1.8 meters tall. That's taller than most grown-ups! Pachycephalosaurus belonged to a group called Marginocephalia, which also includes other horned and frilled dinosaurs. They likely munched on plants, using their small, leaf-shaped teeth to tear off vegetation. Imagine seeing a whole herd of these dome-headed dinos grazing in a prehistoric field!