Pachycephalosaurus fossils have been found in Northwestern USA and Alberta, Canada. Pachycepholasaurs were very strong and had dome-shaped heads with cranial spikes. The Pachycephalosaurus’ skull roof was about 30 times thicker than a human skull!
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Some Quick Facts about the Pachycephalosaurus
| Name | Pachycephalosaurus (meaning “Thick-headed lizard”) |
| Type of dinosaur | Pachycephalosaurid (bone-headed) Dinosauria |
| Territory | Open areas and forests, North America |
| Size | The largest known of its kind, 5-6 feet long, 14-15 feet tall, with weight of about 800-1,000 pounds |
| Color | Light brown, with some reddish areas and spots on its back and rough skin |
| Interesting Characteristics | Dome-headed dinosaur that was bipedal with a thick body and a long tail. Bony knobs stuck out from the back of Pachycephalosaurus skull and small spikes surrounded its nose. |
| Diet | Mostly herbivore, possibly an omnivore |
| Major Threats | Predators and Natural Disasters |
The Pachycephalosaurus’ skull was its most noticeable feature. Like other dome-headed dinosaurs, Pachycephalosaurs used their super thick skull for head-butting.
This behavior not only protected it from predators but was also used to attract mates and assert dominance in the herd. These unusual looking dinos were a lot like the modern-day bighorn sheep.
Could the Pachycephalosaurus Live with a T. rex?
The Pachycephalosaurus lived alongside theropods like the Tyrannosaurus rex, Allosaurus, Troodons, and Velociraptors. These carnivores were the biggest dangers faced by Pachycephalosaurs.
The Pachycephalosaurus could use its thick skulls to protect itself from predators. The T. rex was especially vulnerable to Pachysaurs’ head-butting, because once a T. rex was on its side, it took T. rex a long time to get back up again!
Pachycephalosaurs also lived in the same areas as the Ankylosaurus and Triceratops. The Pachycephalosaurus was actually one of the few bipedal herbivores in the region at the time. Like many herbivorous dinos, these three roamed in loosely formed mixed herds for safety.
A predator faced with an Ankylosaurus, Pachycephalosaurus, and Triceratops would have a hard time fighting all three dinosaur species at once!
Did Pachycephalosaurus eat meat?
Scientists agreed that the Pachycephalosaurus mostly ate plants (like the Pisanosaurus). However, a newly discovered, more complete skull of this dinosaur suggests they may have also eaten meat (like the Tawa Hallae). This scull of a very young dino had a very sharp set of teeth, meaning that young ones were maybe eating other animals.
Were Pachycephalosaurus and Dracorex the Same?
The Pachycephalosaurus also lived with the Dracorex and Stygimoloch. Paleontologists Horner and Goodwin believe Dracorex and Stygimoloch were actually juvenile Pachycepholasaurs. Horner and Goodwin suggested that the domed head and spikes grow later in life.
Since the Dracorex and Stygimoloch fossils that have been found so far are juveniles, there’s no answer yet. There are no juvenile Pachycephalosaurus fossils, as far as we know.
Like all things with paleontology, until there’s enough evidence, we won’t know if Goodwin and Horner were right.
Who Was the Paleontologist who Discovered the Pachycephalosaurus?
Multiple people discovered the Pachycephalosaurus around the same time. In 1931, Charles Gilmore found a partial Pachycephalosaurus skull in Wyoming, which he called Troodon wyomingensis.
In 1938, an almost complete skull was found in Montana’s section of the Hell Creek Formation by William Winkley. And in 1943, paleontologists Barnum Brown and Erich M Schlaikjer renamed the species Pachycephalosaurus wyomingensis.
Starting as early as the 1850s, small remains of Pachycephalosaurus fossils were found throughout the Northwestern USA. In 1859, Geologist Ferdinand Vandiveer found a small bone fragment in the Missouri River in Montana. At the time, he thought it was armor from a reptile or something similar to an armadillo.
In 1872, paleontologist Joseph Leidy named this find Tylosteus. The bone fragment was reexamined in 1985 by Donald Baird and connected to the Pachycephalosaurus. Usually, the older genus name (Tylosteus) would be used. But Baird petitioned to keep the more accurate Pachycephalosaurus and won.
The Pachycephalosaurus might have had some odd features. But all those features worked together to make Pachycephalosaurs one of the most interesting dinos of the Late Mesozoic. Their wide-set eyes gave them binocular vision, which helped them spot danger.
Their small forelimbs were basically useless, but their thick skull surrounded by cranial spikes gave them plenty of protection from predators like the T. rex.