Pachyrhinosaurus canadensis

Pachyrhinosaurus canadensis was a robust horned dinosaur from southern Alberta near the end of the Cretaceous. Unlike Triceratops, it belonged to the short-frilled centrosaurine branch of ceratopsids. Mature skulls replaced the familiar nasal horn with a broad, roughened bony boss and carried additional bosses above the eyes. These surfaces supported keratin in life, but whether that covering formed pads, low domes or taller horn-like structures is unknown. P. canadensis is the type and geologically youngest named Canadian species of Pachyrhinosaurus; the famous Pipestone Creek mass-death assemblage belongs to the distinct species P. lakustai.

Its fossils occur between approximately 73.1 and 71.5 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

The skull was deep and heavily reinforced, with a parrot-like beak at the front and dense dental batteries farther back for slicing vegetation. A broad nasal boss occupied the snout, paired bosses rose above the eyes, and the short frill carried hooks and small marginal ornaments. The neck and torso were muscular, the forelimbs stout and slightly shorter than the hind limbs, and the hands and feet supported a graviportal four-legged stance. Skull ornament changed during growth, so juveniles did not look like scaled-down adults.

• Broad roughened nasal boss replacing a typical nasal horn
• Paired bosses above the eyes in mature individuals
• Short frill edged by hooks and smaller ornaments
• Parrot-like beak and tightly packed dental batteries
• Deep, strongly reinforced skull
• Robust quadrupedal body with columnar limbs

Geologist J. S. Stewart reported a skull beside the Little Bow River east of Carmangay, while O. A. Erdman sent fragments from Scabby Butte to the National Museum of Canada in 1945. Charles M. Sternberg investigated both regions during the 1946 field season and collected additional skull material. In 1950 he named Pachyrhinosaurus canadensis from incomplete skull CMN 8867, with CMN 8866 among the key referred specimens. The fossils came from units historically called the Lower Edmonton and from the St. Mary River Formation; modern work places the main Horseshoe Canyon occurrence in a dated assemblage zone about 73.1–71.5 million years old.

Discovery credit: J. S. Stewart, O. A. Erdman, Charles M. Sternberg.

Naming authors: Charles M. Sternberg.

Pachyrhinosaurus canadensis inhabited coastal plains crossed by rivers near the retreating Western Interior Seaway. The lower Horseshoe Canyon Formation records a shift from warm, wet deltaic habitats toward cooler, seasonally wet and dry lowlands. Conifers, flowering plants, ferns and horsetails supplied vegetation, while hadrosaurs, armoured dinosaurs and tyrannosaurids occupied the wider ecosystem. The St. Mary River sites represent related inland floodplain settings farther south and west.

The beak cropped plants and dental batteries sliced them into manageable pieces. Multi-individual Pachyrhinosaurus sites containing animals of different ages suggest that at least some populations gathered, but several sites belong to other species and a bonebed does not reveal the duration or organisation of a herd. The nasal boss probably carried a keratinous covering and may have served for display or physical interaction. Direct head-butting is possible but not demonstrated, and the exact shape of the living structure is unknown.

• Its name means thick-nosed lizard, referring to the massive nasal boss.
• The rough boss was the bony core of a keratin-covered structure whose living outline is not preserved.
• Pachyrhinosaurus was a centrosaurine, not a close member of the long-frilled Triceratops branch.
• The celebrated Pipestone Creek bonebed preserves P. lakustai rather than P. canadensis.

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1. 01
   Palaeobiology Collections

   Canadian Museum of Nature

   Open source
2. 02
   Pachyrhinosaurus canadensis, representing a new family of the Ceratopsia, from southern Alberta

   Charles M. Sternberg · National Museum of Canada Bulletin 118 · 1950

   Open source
3. 03
   High-precision U–Pb CA–ID–TIMS dating and chronostratigraphy of the dinosaur-rich Horseshoe Canyon Formation

   David A. Eberth, Sandra L. Kamo · Canadian Journal of Earth Sciences 57(10) · 2020

   Open source
4. 04
   Pachyrhinosaurus

   Natural History Museum, London

   Open source