Discovery of Zavacephale rinpoche: The Oldest Known Pachycephalosaur

Paleontologists have unveiled a groundbreaking discovery in Mongolia’s Gobi Desert: a new species of pachycephalosaur named *Zavacephale rinpoche*. This dinosaur, dating back approximately 108 million years to the Early Cretaceous period, is notable for being the oldest and most complete pachycephalosaur fossil ever found. The fossil includes a well-preserved skull, limb and tail bones, and for the first time, hand bones and stomach stones, providing unprecedented insights into the anatomy and biology of this group of dinosaurs.

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The discovery was made by Tsogtbaatar Chinzorig from the Mongolian Academy of Sciences during an expedition in 2019. The fossil was found in the Khuren Dukh locality, an area that, during the Early Cretaceous, was a lush valley with several lakes. The name *Zavacephale* combines the Tibetan word for "root" or "origin" with the Latin word for "head," while *rinpoche* translates to "precious one," reflecting the specimen's remarkable preservation.

Rare ‘Teen’ dinosaur butts into fossil record

*Zavacephale rinpoche* was a juvenile at the time of its death, measuring about three feet long. Despite its young age, it had already developed a fully formed dome on its skull, a characteristic feature of pachycephalosaurs. This dome is believed to have been used for socio-sexual displays rather than for defense against predators. Dr. Lindsay Zanno, a co-author of the study, emphasized that the dome likely served as a means for competition among mates.

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The fossil's completeness allows researchers to couple growth stages with dome development for the first time. The presence of gastroliths, or stomach stones, indicates that *Z. rinpoche* utilized these stones to aid in food digestion, reshaping our understanding of its dietary practices.

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The discovery of *Zavacephale rinpoche* pushes back the fossil record of pachycephalosaurs by at least 15 million years, filling a crucial gap in the evolutionary timeline of these dinosaurs. Previously, most known pachycephalosaurs were found in North America, with limited fossil evidence from earlier periods. This new find suggests that the origins of dome-headed dinosaurs may be traced back to Asia, challenging previous assumptions about their evolutionary history.

Earth & SkyAll That's InterestingRare ‘Teen’ dinosaur butts into fossil record

Dr. Ryan Tucker from Stellenbosch University noted the significance of this find in understanding the evolutionary path of pachycephalosaurs, stating that it provides a clearer picture of their growth patterns and anatomical features.

South African scientist discovers rare dinosaur fossil in Mongolia's Gobi Desert

The research findings were published in the journal *Nature* on September 17, 2025. Chinzorig remarked, “*Z. rinpoche* predates all known pachycephalosaur fossils to date by about 15 million years.” Zanno described the specimen as a “once-in-a-lifetime discovery,” highlighting its importance for understanding the biology and evolution of these enigmatic dinosaurs.

South African scientist discovers rare dinosaur fossil in Mongolia's Gobi DesertRare ‘Teen’ dinosaur butts into fossil recordAll That's Interesting

• “This specimen is a once-in-a-lifetime discovery.” — Dr. Lindsay Zanno, North Carolina State University

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• “rinpoche, such as the hand elements, the stomach stones (gastroliths), and an articulated tail with covered tendons, reshape our understanding of the paleobiology, locomotion, and body plan of these ‘mysterious’ dinosaurs.” — Dr. Tsogtbaatar Chinzorig, Mongolian Academy of Sciences

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• “Zanno commented: The consensus is that these dinosaurs used the dome for socio-sexual behaviors.” — Dr. Lindsay Zanno, North Carolina State University

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The discovery of *Zavacephale rinpoche* not only enriches our understanding of pachycephalosaurs but also opens avenues for further research into their evolutionary history and ecological roles during the Cretaceous period.

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