Wikijunior:Dinosaurs/Pachycephalosaurus

Pachycephalosaurus was a dinosaur which lived in the late Cretaceous period in North America. It gave it's name to a group of dinosaurs called the Pachycephalosauridae. It is most famous for its oddly-shaped head, which has a very unique look.

Anatomy
Pachycephalosaurus was a dome-headed dinosaur. Its huge head housed an incredibly thick skull, a tiny brain, and large eyes. Its rounded skull was up to 10 inches thick (25 cm).

Pachycephalosaurus grew to be about 15 feet long (4.6 m) and may have weighed roughly 950 pounds (430 kg). Pachycephalosaurus probably had a good sense of smell. It had bumpy knobs on its snout and along the rear of its skull. This plant-eater had short forelimbs and a stiff tail (which had a distinctive mesh of interwoven tendons surrounding its rear portion).

What did they look like?
The Pachycephalosaurus was 15-16 feet long. It stood on two legs and had two short arms with five fingers each. However, the most notable thing about its appearance was the large dome on top of its head. This skull was almost a foot thick. It was covered with armor and spikes.

What did they eat?
The Pachycephalosaurus was a vegetarian, despite its intimidating appearance. From its teeth, we have been able to get a good idea of the diet it ate. It is believed to have eaten mostly tough plants, but also sometimes fruit and seeds.

When did they live?
Pachycephalosaurus lived from about 70 to 65 million years ago (Cretaceous) in the Mesozoic era. It was among the last of the dinosaurs to evolve. Like all other dinosaurs that lived at the same time as it, it became extinct about 65 million years ago because of an unknown cause.

How did they move?
Pachycephalosaurus walked on two legs, and was not a very fast dinosaur. When it walked or ran, it probably held its back level to the ground. It may have gone on all fours to forage for low-lying plants.

What was their habitat?
The Pachycephalosaurus was the dinosaur equivalent of many large vegetarians today. It is believed that they lived in a forest in the Cretaceous period.

Where were their fossils found?
Pachycephalosaurus was discovered in 1938 by William Winkley on the family ranch outside of Ekalaka, Montana, USA. It was named Pachycephalosaurus in 1943 by Barnum Brown and Erich M. Schlaikjer. Although complete fossils are rare, many thick skull fragments have been found. Pachycephalosaurus and other pachycephalosaur fossils have been found in Alberta, Canada, the western United States, the Isle of Wight, Mongolia and Madagascar.