Pachycephalosaurus is an herbivorous dinosaur known as the 'head-butting dinosaur' due to its exceptionally thick skull. Scientists have discovered the oldest-ever fossil of a new pachycephalosaur species in Mongolia. This discovery pushes back the pachycephalosaur fossil record by about 15 million years, and its excellent state of preservation has raised expectations among researchers.
A research team led by Professor Lindsay Zanno of the Department of Biological Sciences at North Carolina State University in the U.S. discovered the fossil of the new pachycephalosaur species, dating back to the Cretaceous period about 100.8 million years ago, in the Mongolian desert. They published their findings in the international journal 'Nature' on the 17th (local time). The species was named Zavacephale rinpoche. The name means 'precious one with the roots of a pachycephalosaur.'
Characterized by their thick, dome-shaped skulls and surrounding ornamental structures, pachycephalosaurs are thought to have used their heads for self-defense or social functions like attracting mates. Due to a scarcity of early fossils, most of which are fragmentary, there has been insufficient evidence to fully understand their origin and evolutionary process.
The research team identified Zavacephale rinpoche by analyzing a fossil found in the Khuren Dukh region of Mongolia's Gobi Desert. The individual was small, with a body length of 1 meter and a weight of 5.85 kg, and is analyzed to have been a juvenile at the time of death. Adults are estimated to have reached a body length of 4.3 meters, a height of 2.1 meters, and a weight of about 400 kg.
"The dome-shaped skull developed before the body was fully grown," the research team analyzed, adding, "The development of the skull and the body were separate."
The Zavacephale rinpoche fossil is highly valuable as it is almost completely preserved, including its skull and limbs. It shows little of the skull ornamentation commonly found in other pachycephalosaur fossils. This is expected to provide new clues for scientists debating whether the presence or absence of ornamentation is a difference that distinguishes species or one that is dependent on growth stage.
"The Zavacephale rinpoche fossil reshapes our understanding of pachycephalosaur locomotion and body structure," the research team stated.
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- doi.org/10.1038/s41586-025-09213-6
