Thick-headed lizard

Late Cretaceous – 70 – 65 Mya

North America: Montana, South Dakota, Wyoming

Length: 5.5 meters (18 feet)
Height: 3.1 meters (10 feet)
Weight: 1,814 kg (4,000lb)

The thick domed skull of Pachycephalosaurus protected the small braincase during combat. Flank butting, not head-butting, was likely what occurred during battle as there is no evidence of scars or damage on Pachyrhinosaurus skulls. The bony dome could be up to 25cm (10 inches) thick but it is the domes rear aspect, edged with bony knobs and the short, blunt spikes which projected upward from the snout which gave the most bizarre appearance to this dinosaur.

The small ridged teeth were unable to chew on the tough, fibrous plants that were characteristic of the period and which nourished other dinosaurs. It is thought that Pachycephalosaurus lived on a diet of insects, leaves, seeds and fruit.