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21h ago

Oldest, Most Complete Dome-Headed Dinosaur Unearthed in Mongolia

Bone histology reveals a juvenile with a fully formed dome, reshaping views of pachycephalosaur growth.

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Paleontologist Lindsay Zanno holds the fossilized skull of the Cretaceous Period dome-headed dinosaur named Zavacephale rinpoche, whose remains were found in Mongolia, at the at the Institute of Paleontology, Mongolian Academy of Sciences, in Ulaanbaatar, Mongolia, in this image released on September 17, 2025. Alessandro Chiarenza/Handout via REUTERS THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. MANDATORY CREDIT. NO RESALES. NO ARCHIVES
The fossil was discovered sticking out of the side of a cliff in Mongolia.
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Overview

  • The new species, Zavacephale rinpoche, dates to about 108 million years ago and pushes the pachycephalosaur record back by roughly 14–15 million years.
  • Described in Nature, the skeleton is the most skeletally complete for the group, preserving about 54% of the body including a near-complete skull.
  • Exceptional preservation includes the first pachycephalosaur hand bones, gastroliths, and an articulated tail with covered tendons.
  • CT scans indicate the dome was primarily built from frontal bones, contrasting with later species that integrated more of the skull into the dome.
  • Discovered at the Khuren Dukh locality by lead author Tsogtbaatar Chinzorig, the juvenile measured roughly 1 meter in length and about 5.85 kilograms.