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Beauty or brains? The braincase of Pachyrhinosaurus perotorum and its utility for species-level distinction in the centrosaurine ceratopsid Pachyrhinosaurus

  • Ronald S. Tykoski (a1) and Anthony R. Fiorillo (a1)

The centrosaurine ceratopsid taxon Pachyrhinosaurus is the most speciose of centrosaurines, being represented by at least three species (P. canadensis, P. lakustai, and the recently described P. perotorum) from the late Campanian and early Maastrichtian of North America. The species are readily distinguished from one another by details of easily visible cranio-facial and frill ornamentation, features commonly used to differentiate ceratopsid taxa. Braincase material is also known for all three taxa. We describe the braincase of P. perotorum based on specimens from the Kikak–Tegoseak Quarry of the North Slope of Alaska. We then compare it to braincase and endocranial descriptions of the other Pachyrhinosaurus taxa to test whether there may be useful species-level differences present in these robust parts of the ceratopsid skull. Braincase morphology, including cranial nerve paths through the braincase walls in P. lakustai and P. perotorum, were found to be very similar. Two potential diagnostic differences between taxa were found, although tests based on larger sample sizes will be necessary to verify them. This reinforces the importance of highly visual cranio-facial and frill ornamentation as the best tool for species recognition and phylogenetic reconstruction in ceratopsid dinosaurs.

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