Pachycephalosaurus was a genus of pachycephalosaurid dinosaurs that lived around 75 million years ago during the Upper Cretaceous period. The name Pachycephalosaurus means “thick-headed lizard”, from the Greek words pachys meaning “thick”, kephalos meaning “head”, and sauros meaning “lizard”. It was one of the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event.

Key Facts

Pachycephalosaurus pronunciationpack-i-KEF-al-oh-sore-russ
What does Pachycephalosaurus mean?Thick-headed lizard
Dinosaur typeOrnithopod
On the menuHerbivorous
Length5 meters ( 16 feet)
Height1.8 m (6 feet )
Weight450 kg  (about 900 lbs)
Life expectancyUnknown
Legs used to get aroundBipedal
Estimated top speed24 km/h (15mph)
When they livedUpper Cretaceous era 76-65 million years ago
Where they have been found?Canada, USA

When & Where

Pachycephalosaurus was first described in the early 1850s. Donald Baird made the first discovery in 1859. He was later followed by Ferdinand Vandeveer Hayden, an American fossil collector. The latter unearthed a bone fragment along the source of the Missouri River in the present-day Lance Formation in southeastern Montana. This specimen was thoroughly studied and, in 1872, identified as belonging to the dermal armor of a dinosaur. These findings were, however, disputed when Baird studied the specimen again and identified it as a squamosal—a bone from the back of the skull of Pachycephalosaurus.

The Pachycephalosaurus is one of the best-known dinosaurs due to its abundance of fossil remains and its popular representation in the media. More than 30 specimens have been discovered, making it one of the most commonly found pachycephalosaurids.

Size & Weight

Pachycephalosaurus was a small to medium-sized dinosaur, measuring around 5 meters (16 ft) in length and weighing approximately 450 kilograms ( about 6600 lb). It had a small head with large eyes and a short neck. The body was stocky, with short legs and a long, thick tail. It was covered in spikes and scutes of various sizes and had a large, domed head with a thick layer of bone at the back. It has been speculated that the spikes and scutes on its body may have been used for protection against predators or for display purposes and that it may have used its domed head for butting contests with other members of its species.

Mobility & Diet

Pachycephalosaurus was a bipedal dinosaur, meaning it walked on two legs. It is thought to have had a top speed of around 24 km/h (15mph). It was a herbivore and would have eaten plants, fruits, and leaves.

Interesting Points

  • The Pachycephalosaurus is famous for its large bony dome on its skull, measuring up to 25 cm in thickness.
  • The Pachycephalosaurus had very good eyesight and was capable of binocular vision.
  • Young Pachycephalosaurus had large horns protruding from the back of the skull but shrunk and disappeared as the dome grew. 
  • It was the largest of the bone-headed dinosaurs.

Featured Image Credit: Fred Wierum, CC BY 4.0, via Wikimedia Commons