WASHINGTON, DC.- The Smithsonian’s National Museum of Natural History has acquired a remarkably complete skull of Pachycephalosaurus, a dinosaur famed for its domed head that lived alongside species like Tyrannosaurus rex and Triceratops at the end of the Cretaceous Period around 67 million years ago. The rare fossil was purchased and donated to the museum by Eric and Wendy Schmidt.

Visitors will have a chance to see the new Pachycephalosaurus skull up close starting Dec. 22, when it will be on temporary display in the museum’s FossiLab, a working fossil preparation laboratory in “David H. Koch Hall of Fossils—Deep Time.” The skull will remain on display through Dec. 28 (the museum is closed for the holiday Dec. 25), and it will become part of the permanent exhibition in the coming years.

Pachycephalosaurus, whose scientific name means “thick-headed lizard,” is a popular staple of dinosaur books and documentaries. Paleoartists often depict the bipedal herbivores ramming into their rivals headfirst like modern bighorn sheep. But according to paleontologist Matthew Carrano, the museum’s curator of Dinosauria, Pachycephalosaurus and its relatives remain poorly understood due to their fragmentary fossil record. Most specimens consist primarily of the dinosaurs’ dense head domes.

“This skull is by far the most spectacular specimen of this type of dinosaur that we have at the museum,” Carrano said. “We almost never get to see the animal’s face or the teeth or other parts of the head because they usually have broken away.”

The remarkable skull was unearthed in South Dakota in 2024 and purchased at the Sotheby's Natural History auction earlier this year by the Schmidts, who then gifted the specimen to the Smithsonian in conjunction with an additional donation to support digitization efforts of the National Fossil Collection.

“Thanks to an incredible and generous gift, this scientifically invaluable Pachycephalosaurus skull will remain in the national collection forever enabling researchers to better understand this elusive creature,” said Kirk Johnson, the Sant Director of the museum. “We are excited to display this fossil and introduce this iconic dome-headed dinosaur to museum visitors.”

“When we see an ancient fossil like this one, we are confronted with the story of our planet’s past and can consider how humans fit into Earth’s geologic history in a profoundly different way,” said Wendy Schmidt. “Eric and I hope the digitization project and this rare Pachycephalosaurus skull will provide access to these fossils to anyone, anywhere in the world, and will offer insights into our brief role in our planet’s story of life.”

The fossil was found in rocks of the Hell Creek Formation, a geologic layer that records the 1.5 million years leading up to the asteroid strike that wiped out non-avian dinosaurs 66 million years ago. Over the decades, the Hell Creek Formation has yielded many sensational specimens, including the Nation’s T. rex skeleton that now resides in the museum’s Deep Time Fossil Hall.

Among Hell Creek’s diverse assemblage of dinosaur fossils, Pachycephalosaurus specimens are particularly rare. Its bones account for less than 1% of fossils found in the formation. This may be because Pachycephalosaurus, while capable of reaching 15 feet long, was significantly smaller than multi-ton herbivores like Triceratops and the duck-billed dinosaur Edmontosaurus—but it also may have been less abundant in the local ecosystem.

The new specimen contains nearly the entire skull of the dinosaur, including 32 different cranial bones, several of which had fused together to create the animal’s signature dome. The fossil also contains many of the dinosaur’s teeth, including a set of replacement teeth still growing in its jaws. The fossilized dentition will help paleontologists identify isolated Pachycephalosaurus teeth from the Hell Creek Formation.

Carrano notes that the new skull is one of very few known Pachycephalosaurus skulls that are nearly complete. The rarity of fossil skulls has caused confusion among paleontologists over whether other proposed species of pachycephalosaurs with variations in the knobby horns around their domes are actually juvenile examples of Pachycephalosaurus.

The new skull will be a crucial data point in this ongoing debate. According to Carrano, the specimen probably represents an individual that was not quite fully grown when it died. Examining this skull and comparing it to other pachycephalosaur skulls will provide insights into how these dinosaurs changed as they grew.

The nearly complete skull will join other scientifically significant Pachycephalosaurus specimens in the museum’s collection. These include the fossilized dome that served as the holotype, or name-bearing, specimen when the dinosaur was first scientifically described in 1931.

Carrano plans to CT-scan the new specimen as part of its study. This will allow access to internal structures like the animal’s brain cavity that are hidden deep inside the dinosaur’s thick skull.

“We can understand the shape and size of the brain and the position of each individual bone, which is really difficult to do when the outside looks basically like a bowling ball,” he said.

The Pachycephalosaurus skull will also be surface scanned to create a digital copy of the specimen, which will allow researchers to study the fossil in detail from anywhere in the world. This is part of a larger five-year effort to digitize a thousand of the museum’s most notable fossils, making a cross-section of the Smithsonian’s world class paleontology collection easily accessible online. The Schmidts’ gift has also enabled this important digitization project.

Carrano looks forward to uncovering the scientific insights preserved inside the Pachycephalosaurus skull.

“This is definitely the best part of being a curator—getting to study a new specimen and knowing that it is going to live here in the national collection forever.”