A newly discovered fossil from the Cretaceous of Mongolia tells us an interesting story about the purported head butting behaviour of dinosaurs. Pachycephalosaurs are famous for their thick domed heads but it has been disputed how or when this evolved. The beautifully preserved Zavacephale rinpoche has a well preserved skull and dome but also loads of details of the body and tail as well. What is suprising is that this individual is much smaller, and occurs much earlier, than other pachycephalosaurs. We take a look at this new fossil and what this means for interpreting the evolution of dinosaur behaviour.  This week's paper is "A domed pachycephalosaur from the early Cretaceous of Mongolia" by Tsogtbaatar Chinzorig and colleagues from Mongolia and North Carolina, published in Nature in September 2025. https://doi.org/10.1038/s41586-025-09213-6 Wide screen palaeoart by Masaya Hattori.

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