The Acrotholus was a herbivorous pachycephalosaurid dinosaur that lived in what is now Canada during the Upper Cretaceous period, about 85 million years ago. Known for its large, flat head and thick skull bones, the Acrotholus was a small dinosaur, only about the size of a coyote. It had a dome-shaped head, which is thought to have been used for display purposes or head-butting contests with other members of its species.

Key Facts

Acrotholus pronunciationACK-roe-THO-luss
What does Acrotholus mean?Highest Dome
Dinosaur typePachycephalosauria
On the menuHerbivorous
Length1.8 meters
Height0.8 meters
Weight40 kg
Life expectancyUnknown
Legs used to get aroundBipedal
Estimated top speedUnknown
When they livedUpper Cretaceous, 85 million years ago
Where they have been found?Canada

When & Where

In 2008, a student accompanying two paleontologists on a fossil-hunting expedition in southern Alberta, Canada, discovered the skull of an Acrotholus dinosaur. This was in the Milk River Formation, which dates back to the Santonian stage of the Upper Cretaceous period—about 85 million years ago.

This partial skull revealed the presence of a thick, bony crest on the head of the Acrotholus. It was the first time such a feature had been found in a pachycephalosaurid dinosaur. To date, the skull remains the only known specimen of Acrotholus.

Size & Weight

This small dinosaur was only about the size of a coyote, measuring 1.8 meters in length and 0.8 meters in height. It weighed an estimated 40 kg.

Mobility & Diet

The Acrotholus, like other pachycephalosaurids, was a herbivore. It probably fed on low-lying plants and shrubs. To get around, it used its two legs to walk on land. However, due to the lack of fossils, its top speed is unknown.

Interesting Points

  • The Acrotholus was characterized by its large, dome-shaped head, resistant to pre-displacement impact. It is thought that the function of this thick, bony crest was either for display purposes or head-butting contests.
  • Contrary to its terrestrial lifestyle, scientists believe the Acrotholus may have lived along the shores of an inland sea known as the Western Interior Seaway. This theory is based on the fact that its fossils have been found in areas once covered by this shallow sea.
  • The Acrotholus is one of the oldest known pachycephalosaurids and is thought to be the ancestor of other dome-headed dinosaurs, such as Pachycephalosaurus.

Featured Image Credit: Nobu Tamura, CC BY-SA 4.0, via Wikimedia Commons