Oldest near-complete dome-headed dinosaur fossil unearthed in Mongolia

Paleontologists have unearthed the oldest near-complete fossil of a dome-headed dinosaur, belonging to a newly named pachycephalosaur species Zavacephale rinpoche. The specimen dates to roughly 108 to 115 million years ago and was found at the Khuren Dukh locality in Mongolia's Eastern Gobi Basin, a region that was dotted with lakes and cliffs during its prehistoric heyday.

The skeleton is the oldest and most complete pachycephalosaur skeleton recovered to date. The team indicates the fossil likely represents a teenage juvenile about 3 feet long and weighing roughly 13 pounds. The dome-like skull shows substantial cranial development for its size, and the skull itself was small enough to fit in the palm of a researcher’s hand, underscoring how compact these domed heads could be in smaller individuals.

In a paper published in Nature on Wednesday, researchers identify Zavacephale rinpoche as the earliest known divergence from pachycephalosaurians. The find pushes back evidence of a fully developed frontoparietal dome by at least 14 million years, offering new insight into how cranial domes evolved in this group. Lindsay Zanno, associate research professor at North Carolina State University and a co-author of the Nature paper, described the find as remarkable for its age and completeness. Lead author Tsogtbaatar Chinzorig noted that the specimen helps illuminate the functional roles of domed skulls in activities such as mating displays and social interactions, in addition to defense.

Located in the Eastern Gobi Basin, the Khuren Dukh site preserves a landscape that researchers say included lakes and cliffs in the dinosaur-era environment, making the discovery a critical data point for understanding pachycephalosaur evolution during the Late Cretaceous. Researchers affiliated with the North Carolina Museum of Natural Sciences contributed to the study, which adds a missing piece to the broader picture of dome-headed dinosaurs.