Even though it did not have the elaborate horns of some ceratopsians like Einiosaurus, Pachyrhinosaurus has become a favourite amongst ceratopsian dinosaur enthusiasts because of the large bony growth called a boss that is present on top of its snout. A second smaller boss was also present over the eyes and is sometimes close to the nasal boss. Pachyrhinosaurus still possessed some small horns, particularly around the edges of the frill. Some of these characteristics are shared amongst the Pachyrhinosaurus species while some are unique to just one species.
Distinguishing characteristics of Pachyrhinosaurus species
Distinguishing feature P. canadensis P. lakustai P. perotorum
Eye and snout bosses almost together? Yes No Yes
Two curved backwards pointing horns on frill? Yes Sometimes No
Jagged 'comb' extension on tip of nasal boss? No Yes Yes
Narrow dome in centre of upper portion of nasal boss? No No Yes
Pommel on the front of nasal boss? No Yes No
Two flattened horns that point forwards and down from top of frill? Yes No No
Flat and rounded nasal boss? Yes No No
Comb-like horn rising from middle of frill behind the eyes? No Yes No
Known formations for the species Horseshoe Canyon Bearpaw, Horseshoe canyon Prince Creek
The first Pachyrhinosaurus fossils were actually discovered way back in 1880, but they did not get the attention they deserved until the late 1940s which would result in the establishment of the type species in 1950. The most significant discovery relating to Pachyrhinosaurus however was the excavation of the Pipestone Creek bone bed in the late eighties (originally discovered by Al Lakusta in 1972) which ultimately yielded three and a half thousand Pachyrhinosaurus bones as well as fourteen skulls. These bones represent individuals of all ages from fully grown adults to juveniles, suggesting that ceratopsians like Pachyrhinosaurus moved around in herds, possibly as a protection against large tyrannosaurid predators like Albertosaurus.
One explanation for this bone bed occurring is that the Pachyrhinosaurus were crossing a river that may have been swollen with flood water, resulting in treacherous conditions that claimed the lives of many of the herd. Similar bone beds are also known for other ceratopsian dinosaurs like Centrosaurus and Styracosaurus. Specimens from this bone bed display a mix of convex (curved outward) and concave (curved inward) bosses. While speculation for this has been cited as representing male and female specimens, the differences may have been caused by erosion of the material. Individuals from this bone bed were named Pachyrhinosaurus lakustai after Al Lakusta.
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