Teenage “Dick-head” Dinosaur Rewrites Pachycephalosaur Evolution Timeline
ULAANBAAR, Mongolia – September 18, 2025 – A newly discovered fossil in Mongolia reveals Zavacephale Rinpoche, a teenage Pachycephalosaur, represents the earliest known evolutionary form of the iconic dome-headed dinosaur. The find pushes back the timeline for the development of this distinctive feature and provides unprecedented insights into the growth and anatomy of these “bone-headed” dinosaurs.
The fossil, analyzed by a team led by paleontologists from North Carolina State university and the Mongolian Academy of Sciences, dates to a period earlier than previously understood for advanced Pachycephalosaurs. Researchers persistent the specimen was approximately one metre long and weighed 5.85 kilograms, significantly smaller than adult Pachycephalosaurs which could reach 4.30 meters in length and weigh up to 410 kilograms. This, coupled with the bone structure, indicates Zavacephale Rinpoche was a juvenile.
“Zavacephale Rinpoche gives us an unprecedented insight into the anatomy and biology of the Pachycephalosaurs,” saeid Dr. Lindsay Zanno. The fossil exhibits a well-developed, though less ornate, skull thickening characteristic of the species. Researchers also discovered evidence the dinosaur used gastroliths - stomach stones – to aid in food digestion, a previously unknown trait. Furthermore, the team confirmed these dinosaurs possessed a flexible neck with covered tendons.
“Since the head decorations change in the course of growth,it has so far been difficult to determine the respective kind or the development of an animal,” explained Zanno. ”Now we can do that for the first time and connect the development of the dome structure.”
Paleontologist Chinzorig added, “Zavacephale Rinpoche is an important specimen for understanding the development of the crests of Pachycephalosaur.” The revelation fills critical knowledge gaps regarding the species’ timeline, lifespan, and anatomical development.
The research was published in Nature (2025; DOI: 10.1038/S41586-025-09213-6).
Sources: North Carolina State University, Nature.