A rare dinosaur fossil from Mongolia’s Gobi Desert is giving scientists new insight into one of the most mysterious groups of dinosaurs.
The fossil belongs to a new species of pachycephalosaur—a group of plant-eating dinosaurs famous for their large, domed skulls.
What makes this specimen special is that it is both the oldest and most complete pachycephalosaur ever found, dating back 108 million years to the Early Cretaceous period.
The new species has been named Zavacephale rinpoche, which translates to “precious root head.” Its skull was discovered partially exposed on a cliff, gleaming like a jewel.
At the time Z. rinpoche lived, the Gobi Desert was a lush valley dotted with lakes and surrounded by rocky cliffs.
While adult pachycephalosaurs could grow up to 14 feet long and weigh close to 900 pounds, this specimen was only about three feet long when it died—still a juvenile.
Despite its young age, Z. rinpoche already had a fully developed cranial dome.
This detail is important because paleontologists have long debated whether differences in pachycephalosaur skulls reflect separate species or simply different stages of growth.
Since most pachycephalosaur fossils are just fragments of skulls, this complete skeleton provides the first chance to connect dome development directly with growth stage. By studying growth rings in the leg bone, researchers confirmed the animal was a teenager at the time of its death.
“This fossil is spectacular,” says Lindsay Zanno of North Carolina State University and the North Carolina Museum of Natural Sciences.
“It lets us couple growth stage with dome development for the first time and fills in a major gap in the evolutionary history of these dinosaurs.”
Pachycephalosaurs are often imagined headbutting each other in dramatic contests, though scientists believe their domes were used mainly for display and competition for mates rather than defense. “If you need to headbutt yourself into a relationship, it’s a good idea to start rehearsing early,” Zanno jokes.
Beyond the skull, the fossil also preserves rare details that shed light on the animal’s biology. Researchers found stomach stones, or gastroliths, which the dinosaur likely used to grind its food, much like modern birds do. The skeleton also included hand bones and a tail with tendons still in place, offering a more complete picture of how pachycephalosaurs moved and lived.
Lead author Tsogtbaatar Chinzorig of the Mongolian Academy of Sciences calls the discovery “a once-in-a-lifetime find.” Not only does Z. rinpoche push the origin of pachycephalosaurs back by at least 15 million years, but it also gives scientists their best look yet at how these dome-headed dinosaurs grew and behaved.
The study, published in Nature with support from the National Geographic Society, brings scientists one step closer to understanding these “mysterious” dinosaurs that once roamed Mongolia’s ancient landscapes.
