Pachycephalosaurus

Pachycephalosaurus was an unusual-looking dinosaur. It stood on two legs, had a beak for cropping plants and had a large bony dome on its head surrounded by spikes and bumps.

Some scientists think that the animal used its hard dome in head-butting contests, similar to the way modern-day rams use their horns.

Other experts think that the head dome may have been used for display. Perhaps it had many uses - like the antlers of modern deer, which are used both for fighting and for display.

Pachycephalosaurus lived in the Late Cretaceous Period of North America. Its fossils have been found in Montana, South Dakota, Wyoming and Alberta.

The environment was subtropical, with warm humid air and many flowering plants.

Pachycephalosaurus shared its habitat with many other dinosaurs, including Tyrannosaurus, Triceratops and Ankylosaurus.

Experts think Pachycephalosaurus was herbivorous, living on a diet of leaves, fruit and seeds. But nobody knows for sure.

Some of the dinosaur's front teeth look a bit like those of carnivorous dinosaurs. This has led some scientists to suggest that Pachycephalosaurus might have eaten meat, too.

For many years, we thought that Stygimoloch, Dracorex and Pachycephalosaurus were all separate, but possibly closely related, dinosaurs.

Now, most scientists believe that Stygimoloch and Dracorex were younger forms of Pachycephalosaurus. So those dinosaur names aren't often used.

An American fossil collector named Ferdinand Vandeveer Hayden found the first ever Pachycephalosaurus fragment around 1860. Experts at the time thought it might be from an armadillo-like creature. They named it Tylosteus.

The name Pachycephalosaurus was created in 1943 by Barnum Brown and Erich Maren Schlaikjer, after more fossils were discovered.

It wasn't realised until the 1980s that the 'Tylosteus' fossil belonged to Pachycephalosaurus.