Pachyrhinosaurus

Pachyrhinosaurus is a centrosaurine ceratopsid that differs from its close relatives by having a massive bony nasal boss instead of the typical nasal horn. This thick, rugose plate of bone covered the animal's snout. Its other skull features were typical for a centrosaurine: a parrot-like beak, complex dental batteries, and fleshy cheeks. Its parietal-squamosal frill was adorned with various horns and spikes, with the specific arrangement of these ornaments varying by species. Like its relatives, it was a robust quadruped.

Paleontologists universally recognise three species. P. canadensis is the type species. P. lakustai was described in 2008 from the famous Pipestone Creek bonebed, and P. perotorum was identified in 2012 from the Prince Creek Formation in Alaska. Each species possessed a unique boss-and-spike pattern, which likely served for species recognition within groups.

Adults typically reached 6–8 m in length and weighed between 3 and 4 tonnes, making them similar in size to other large centrosaurines.

The Pipestone Creek bonebed in Alberta's Wapiti Formation contains the remains of thousands of Pachyrhinosaurus lakustai individuals. This is one of the largest known ceratopsian fossil sites. Researchers believe the bonebed resulted from a mass-drowning event as a migrating herd attempted to cross a river. Finds like this provide strong evidence that these dinosaurs lived in massive, mixed-age herds and engaged in synchronised migrations across the Late Cretaceous landscape.

Fossils of P. perotorum from the Prince Creek Formation in Alaska are particularly notable. They represent a population that lived year-round at high latitudes (approximately 75–80°N), surviving the long periods of winter darkness in the Arctic. Their nasal bosses and elaborate frills probably functioned as display structures for species recognition. While they may have been used in combat, this was likely a secondary role. Healed wounds found on adult skulls suggest that these dinosaurs engaged in intraspecific contests such as frill-pushing.

• Pipestone Creek bonebed — thousands of P. lakustai individuals, Pipestone Creek Dinosaur Initiative / Philip J. Currie Dinosaur Museum, Alberta.
• NMC 8867 — P. canadensis holotype, Canadian Museum of Nature.
• Prince Creek Formation material — P. perotorum holotype, University of Alaska Museum of the North.

Species count — three species widely accepted. Boss vs horn — the replacement of the nasal horn by a boss is unique among centrosaurines; functional implications (display/combat) debated. Migration vs residency — Alaskan populations may have migrated south seasonally or lived year-round; current evidence (Fiorillo & Tykoski 2012) supports year-round residency at high latitudes.

Pachyrhinosaurus gained mainstream recognition in Walking with Dinosaurs: The 3D Movie (2013), where it served as the protagonist's species. It also appears in Prehistoric Planet (2022). Earlier, it was less famous than Triceratops or Styracosaurus despite the dramatic discoveries at Pipestone Creek.

• ceratopsia
• styracosaurus
• centrosaurus
• triceratops

• Sternberg, C. M. (1950). Pachyrhinosaurus canadensis, representing a new family of the Ceratopsia. Bulletin of the National Museum of Canada, 118, 109–120.
• Fiorillo, A. R., & Tykoski, R. S. (2012). A new Maastrichtian species of the centrosaurine ceratopsid Pachyrhinosaurus from the North Slope of Alaska. Acta Palaeontologica Polonica, 57, 561–573.
• Currie, P. J., Langston, W., & Tanke, D. H. (2008). A new horned dinosaur from an Upper Cretaceous bone bed in Alberta. NRC Research Press.
• Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press.