The Smithsonian’s National Museum of Natural History has added a new, rare fossil to its collection: a dome-shaped skull of a Pachycephalosaurus, a type of dinosaur that lived about 67 million years ago.

The fossil was donated to the museum by philanthropists Eric and Wendy Schmidt. (Eric Schmidt was the CEO of Google until 2011.) The Schmidts purchased the skull from Sotheby’s for $1.7 million in July. It was excavated in 2024 from the Hell Creek Formation, an area known for fossil discoveries from the Upper Cretaceous and Early Paleocene eras in Perkins County, South Dakota.  

The 21-inch-long skull is nearly complete and includes 32 fused cranial bones and many teeth. Remains of this particular dinosaur—a bipedal herbivore whose scientific name means “thick-headed lizard”) are quite rare, and make up less than 1% of the fossils founds in the Hell Creek Formation.

Paleontologist Matthew Carrano, the Smithsonian’s Dinosauria curator, said in a statement that “[t]his skull is by far the most spectacular specimen of this type of dinosaur that we have at the museum. We almost never...