Pachycephalosaurus was discovered in 1943 in Montana. Its name means “thick-headed reptile”. It is part of the pachycephalosauridae family, which includes several herbivorous dinosaurs with this bump on the skull. That of the pachycephalosaurus could reach 25 cm in thickness.
It was long thought that it used this to charge headlong into each other. Today, this theory is being questioned, as the skulls would not have been able to withstand such impacts. The rounded shape of this bump is not suitable, and the two bumps would have slid against each other.
Another hypothesis is that it was used during mating displays and that the most developed skull would attract females. This bump may also have been used to protect against predators.
This dinosaur moved on its two hind legs and was bipedal. It had 5 fingers on each hand that it used to catch its food. It mainly fed on ferns, plants, conifers, and flowers. It lived in groups to protect itself from predators. Juveniles weighed between 147 and 308 kg, and subadults between 308 and 406 kg.
It is one of the last dinosaurs to have lived before the extinction of this group. It lived alongside Tyrannosaurus, Triceratops, and Ankylosaurus.