Cool Finds

Paleontologists Discover Earliest Known Dome-Headed Dinosaur in Excellent Condition, Shedding Light on Its Mysterious Anatomy

Most of what researchers previously knew about the iconic Cretaceous dinosaurs came from their domed heads, which endured better than the rest of their skeletons

Margherita Bassi | Daily Correspondent

September 22, 2025

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Dome-headed dinosaurs, officially called pachycephalosaurs, are one of the “most enigmatic” creatures from the Cretaceous (145 million to 66 million years ago). While these herbivores often appear in popular culture, almost everything about their anatomy—except for their hard heads—has largely remained a paleontological mystery, until now.

Researchers working in Mongolia discovered a new dome-headed dinosaur species, which they named Zavacephale rinpoche. As detailed in a study published last week in the journal Nature, the fossil also represents the oldest and most complete pachycephalosaur to date, filling in critical gaps in our understanding of their biology.

“For those of us who study the dome-headed dinosaurs, Zavacephale is the specimen we have all been waiting for,” David Evans, a paleontologist at the Royal Ontario Museum who did not participate in the study, tells the New York Times’ Annie Roth. “This is a very exciting fossil that helps illuminate the early evolutionary history of this famous, yet poorly understood, group of dinosaurs.”

Zavacephale rinpoche lived in what today is the Gobi Desert around 108 million to 115 million years ago. That makes the fossil around 15 million years older than all known pachycephalosaur specimens. The team suggests it was a juvenile, at just around three feet long. Its diminutive size stands in stark contrast to other pachycephalosaurs, which scientists estimate could max out at about 14 feet long and 7 feet tall as adults.

Before now, most of what paleontologists knew about pachycephalosaurs was based on their tough, domed heads. That’s because the domes could better fossilize and endure millions of years of preservation, compared to the rest of the body.

“If you want to imagine a pachycephalosaur skull, think of half a bowling ball supported by toothpicks,” study co-author Lindsay Zanno, a paleontologist at the North Carolina Museum of Natural Sciences, tells National Geographic’s Riley Black. “Now imagine dropping that in a river. What do you think will survive the journey? Most likely just the dome.” And while some pachycephalosaurs grew to be large, she adds that many were small with fragile skeletons, making it even harder for their remains to stand the test of time.

Due to the limited fossil record, scientists previously knew next to nothing about dome-headed dinosaurs’ basic anatomy, including their arms and digestive systems. As such, the researchers were excited to find a fossil with a largely complete skeleton—including a hand and full tail, both of which are a first for pachycephalosaurs.

The hand bones were so surprisingly small that Zanno says the team first suspected them to be contents from the dinosaur’s gut, per the New York Times. Instead, they found stones, also known as gastroliths, in its stomach, which the animal would have swallowed to help grind up tough food.

Growth rings in the dinosaur’s bones allowed the team to run tests that would determine the creature’s biological age. These revealed that the Z. rinpoche specimen was young—but it already featured a complete dome on its head. This indicates that the dome developed faster than other parts of the dinosaur’s skeleton did.

“The consensus is that these dinosaurs used the dome for socio-sexual behaviors,” Zanno says in a statement. “The domes wouldn’t have helped against predators or for temperature regulation, so they were most likely for showing off and competing for mates. If you need to headbutt yourself into a relationship, it’s a good idea to start rehearsing early.”

Ultimately, Z. rinpoche indicates that pachycephalosaurs may have been talented headbutters millions of years earlier than previously known. “At the end of the day, you have to hand it to pachycephalosaurs,” Zanno tells Reuters’ Will Dunham. “When it comes to flashy headgear, they didn’t phone it in.”

Margherita Bassi | Read More

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.