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4h ago

Oldest, Most Complete Pachycephalosaur Unearthed in Mongolia

The juvenile fossil shows its head dome matured early, offering a new window into pachycephalosaur development.

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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

  • Researchers named the species Zavacephale rinpoche and dated it to about 108 million years ago from Mongolia’s Khuren Dukh Formation, publishing the description in Nature on September 17.
  • The skeleton is the most complete pachycephalosaur yet, preserving the clade’s first known hand bones, stomach stones and an articulated tail with tendons.
  • CT scans and bone histology indicate the individual was still growing yet carried a fully formed cranial dome.
  • The find pushes definitive evidence of dome-headed dinosaurs back by roughly 14–15 million years and recovers Zavacephale as an early-diverging member of the group.
  • Analyses suggest early dome evolution followed a frontal-first pattern and support the interpretation of the dome as a socio-sexual display structure.