This Dinosaur’ Skull Was 10 Inches Thick, And A Deadly Weapon

Written by Austin S.
Updated: July 11, 2022
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Dinosaurs are one of evolution’s interesting creatures. They were apex predators and one of the most diverse species of their time. They belong to a class of archosaurs that includes mammals, birds, and reptiles.

The Mesozoic era featured the advent of dinosaurs and the Jurassic period saw them rise to the top of the food chain. Dinosaurs ruled the land and the oceans, and they evolved more species. Some dinosaurs from earlier stages also flourished with the dawn of dinosaur dominance.

Pachycephalosaurus is one of the dinosaurs from the early Mesozoic era. It evolved before the Jurassic period when dinosaurs dominated. This dinosaur was unique for its thick skull that was first mistaken for a dinosaur kneecap. There have been few fossil discoveries of this dinosaur. This article will discuss what the Pachycephalosaurus was, what it looked like, how it lived, and went extinct.

Description & Size

Pachycephalosaurus is a dinosaur from the Maastrichtian stage of the Late Cretaceous period. It existed between about 72 to 66 million years ago. This period was during the Mesozoic era, which is famous as the age of dinosaurs. Pachycephalosaurus belongs to a group of dinosaurs called pachycephalosaurids. It got its name from Greek, and it means thick-headed lizard. It was first discovered near the Missouri River in the late 1850s.

Pachycephalosaurus had two short forelimbs with five claws, while its two long legs had three claws. A unique feature is its head which had a dome shape and was very thick. Pachycephalosaurus’ skull was initially misidentified as a dinosaur kneecap because of the dome shape of its head. Its skull was about 30 times thicker than a human skull. Some key details about the Pachycephalosaurus are:

  • Length – about 15 feet long
  • Height – about six feet
  • Weight – about 900 lb
  • Family – Pachycephalosauridae
  • Attributes – domed head shape, bony head bumps, very thick skull, and scaly skin

What Pachycephalosaurus looked like

Pachycephalosaurus was a bipedal dinosaur that likely evolved from Hypsilophodon. It had a short and thick neck with a stiff and heavy tail. The dome on its head is the skull part that houses its brain. Around the dome were upward-facing bony bumps. Pachycephalosaurus likely had a good vision with its forward-facing and round eye sockets. This feature also means it likely had binocular vision.

Pachycephalosaurus had a small brain and a beaked snout. It had tiny teeth with crowns in leaf shape. Younger versions of Pachycephalosaurus possessed flatter skulls. As the Pachycephalosaurus grew, the bony bumps around its head dome reduced. Pachycephalosaurus’ bulky body was covered with scaly skin.

Pachycephalosaurus reproduced by laying eggs. There are two contentions to the reason and use for its thick skull. Scientists believed that it used its skull for a head ramming mating contest. There’s also a suggestion that it was used to flank other dinosaurs when asserting territorial dominance. 

Pachycephalosaurus belongs to the Pachycephalosaurs group. Two other species from this group are; Stygimoloch spinifer and Dracorex hogwartsia.


The Pachycephalosaurus was a bipedal dinosaur with a beaked snout and forward-facing eyes.

©Daniel Eskridge/

Diet – What Did the Pachycephalosaurus Eat?

Pachycephalosaurus did not have any predatory abilities. It was an omnivore. Its diet likely included seeds, fruits, and soft plants. There are suggestions that it likely ate insects too. It had small teeth that weren’t tough enough for chewing fibrous plants. Pachycephalosaurus’ small sharp teeth likely chewed on angiosperm plants easily.

There are suggestions that the younger ones likely ate on smaller animals too. These smaller animals include lizards, frogs, smaller dinosaurs, and salamanders. As they grow, they convert to a strict herbivore diet. They also fed on ferns and bushes around their environment.

Habitat – When and Where the Pachycephalosaurus Lived

Pachycephalosaurus lived during the Late Cretaceous period. It lived in the regions that are today’s North America. It lived in forests, fields, lowlands, meadows, woods, plans, and grasslands of North America. Pachycephalosaurus was a land animal and a herbivore. It means it likely lived around vegetation for easy access to food.

This dinosaur lived in the lush and warm regions between the inland seaway and Rocky mountains of the late Cretaceous period. Specific locations it likely lived in include North Dakota, Wyoming, Montana, and South Dakota. Some species of the time lived in New Mexico, Utah, and south of Alberta.

Threats and Predators to the Pachycephalosaurus

Pachycephalosaurus was prey to many significant predators of the period. It had no features for attacking other animals. It was a small animal that couldn’t take on predators of its size. Pachycephalosaurus did not have big and sharp teeth for tearing into its predator’s flesh. It shows that Pachycephalosaurus would have opted to run from its predators. 

Pachycephalosaurus’ thick skull forms its defense mechanism against predators. When cornered, it starts to ram into its predator with its thick skull before trying to escape. The thick skull also protects their brain from damage and bites. Pachycephalosaurus’ skull and speculated speed would have been its only protection against predators. 

Pachycephalosaurus was prey to larger dinosaurs of its time. These dinosaurs include; Allosaurus, Baryonyx, Velociraptors, Carnotaurus, and Dilophosaurus. Pachycephalosaurus was also prey to the fearsome Tyrannosaurus rex it lived with.

Discoveries and Fossils – Where the Pachycephalosaurus Was Found

The first Pachycephalosaurus was discovered by Ferdinand Vandeveer between 1859 and 1860 near the Missouri River. Another fossil was discovered by William Winkley in Montana in the year 1938. Pachycephalosaurus fossils were present in North America. This dinosaur lived in a region which is today’s North American continent.

Only one skull fossil of this dinosaur was ever found. It was identified and described from other fragments that geologists found. Fossils were present in Alberta, Wyoming, South Dakota, and North Dakota. Other fossils were present in Madagascar, Canada, and Mongolia.

Pachycephalosaurus skull

The first Pachycephalosaurus was discovered by Ferdinand Vandeveer between 1859 and 1860 near the Missouri River.


Extinction – When Did the Pachycephalosaurus Die Out?

Pachycephalosaurus lived between the Campanian and Maastrichtian ages of the Cretaceous period. They existed for about 7 million years. Pachycephalosaurus existed with dinosaurs like Ankylosaurus, tyrannosaurus rex, and Triceratops. These animals went extinct when a meteorite hit 66 million years ago.

Pachycephalosaurus died during the extinction event that borders the Cretaceous and Paleogene periods. This extinction event also caused the extinction of dinosaurs from the earth.

Similar Animals to the Pachycephalosaurus

Pachycephalosaurus existed during the age of dinosaurs. It existed with many dinosaurs with similar features and lived in the same region. Dinosaurs diversified into the seas and the air during this era. Some similar animals to the Pachycephalosaurus are:

Tyrannosaurus rex

Tyrannosaurus rex alongside the Pachycephalosaurus. The name means tyrant lizard, which describes its dominance in its era. It’s a muscular dinosaur that grew to 40 feet and weighed about 17,000 lb. Like the Pachycephalosaurus, it had two solid hind limbs and two short forelimbs. It was also fast and could run at 20 mph. Tyrannosaurus rex’s bite force is about 12,000 psi. Unlike the Pachycephalosaurus, T. Rex was a carnivore.


Velociraptors are one of the small dinosaurs of the Mesozoic era. They lived around 70 million years ago in today’s Mongolia. It could grow to about 7 feet long and 1.5 feet high. Scientists estimate its weight to be about 33lb. They had four claws which it used like modern birds use talons. While it was a feathered animal, velociraptors could not take flight like their ancestors likely did.


Dromaeosaurs existed between 145 to 65 million years ago during the Cretaceous period. It is also a bipedal dinosaur with two long hindlimbs and two shorter forelimbs. The second toe of the Dromaeosaur’s foot had a special talon used for attacking prey. This deadly talon could grow up to 5 inches, as in the Deinonychus. Dromaeosaur was about 10 feet long, 6 feet tall, and weighed about 155lb.


Albertosaurus is a theropod dinosaur that lived in the late Cretaceous period. This period was between 71 to 68 million years ago. It belongs to the Tyrannosauridae family. It could grow up to 33 feet long and weigh about 5000 lb. This dinosaur was also discovered in the Alberta region of Canada. It was a fearsome predator in its region during its time.


Carnotaurus is a theropod dinosaur from the Late Cretaceous period. This dinosaur lived between 72 to 69 million years ago. It was about 29 feet long and weighed about 2,200 lb. It’s a part of the Abelisauridae family. It was a bipedal dinosaur with short forelimbs and long hindlimbs like the Pachycephalosaurus. Carnotaurus had two horns on its eyes that were about 6 inches long. It was a carnival=orous dinosaur that had reptilian and scaly skin.


Pachycephalosaurus is an interesting dinosaur with its unique head shape and thickness. It was a medium-sized dinosaur. Pachycephalosaurus lived its herbivore life alongside T.rexes and Velociraptors. It went extinct with the Cretaceous-Paleogene extinction event.

Up Next:

Discover more ancient animals that have been wiped off the earth. Some of these animals have traits you will see in today’s ecosystem. We offer more articles on ancient animals and events on this site.

The photo featured at the top of this post is © Daniel Eskridge/

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About the Author

Growing up in rural New England on a small scale farm gave me a lifelong passion for animals. I love learning about new wild animal species, habitats, animal evolutions, dogs, cats, and more. I've always been surrounded by pets and believe the best dog and best cat products are important to keeping our animals happy and healthy. It's my mission to help you learn more about wild animals, and how to care for your pets better with carefully reviewed products.

FAQs (Frequently Asked Questions) 

Did Pachycephalosaurus head-butt like today’s rams and sheep?

Scientists believe that Pachycephalosaurus did not ram heads as today’s rams do. Pachycephalosaurus’ thick conical skull meant that ramming heads would lead to head spillage. Head spillage is when the head tilts quickly in a head-on collision. It could have caused Pachycephalosaurus’ neck to snap. Scientists believe that Pachycephalosaurus flanked other Pachycephalosauruses with headbutts.

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