Pachyrhinosaurus

Phylogeny: Dinosauria > Ornithischia > Genasauria > Neornithischia > Cerapoda > Marginocephalia > Ceratopsia > Neoceratopsia > Coronosauria > Ceratopsoidea > Ceratopsidae > Centrosaurinae > Pachyrhinosaurini

Overview: Ceratopsid dinosaurs are famous for their cranial ornamentation, possessing elongated frills, hornlets, spikes and horns. Even among such animals, Pachyrhinosaurus was quite unusual. It had no prominent brow or nasal horns, but it did possess a huge, thickened mass of bone over the snout, above its parrot-like beak. Said mass, referred to as a “boss”, typically had a roughened texture and was probably the base for some larger structure made of keratin. The full scale of said structure is unknown, as is its shape. This shape probably varied between the three main species of Pachyrhinosaurus. Described as a genus in 1950, Pachyrhinosaurus was named after its nasal boss, with its generic moniker meaning “thick-nosed lizard” in Greek. The first remains, mainly consisting of skull material, had been found a few years earlier in Canada’s Horseshoe Canyon Formation. In the years to come, many other Pachyrhinosaurus specimens would be found, some as far away as northern Alaska, revealing the genus to have had a wide range. Some evidence suggests it lived in large herds, which may’ve migrated along the coast of the now lost Western Interior Seaway.

The three known species of Pachyrhinosaurus are Pachyrhinosaurus canadensis, Pachyrhinosaurus lakustai and Pachyrhinosaurus perotorum. Among these, the first is the type species, while remains of P. lakustai come from a similar region, but date to somewhat older rock layers. P. perotorum is known from Alaska’s Prince Creek Formation. They can be differentiated by their skull anatomy. All three have short, rounded frills with curving hornlets at the apex, but these vary in shape and form. The same was also true for the nasal boss. For instance, P. lakustai often sported a small hornlet in the middle of its frill, not seen on its relatives, while the nasal boss on P. perotorum tended to have a small dome-like structure at the back. In all species, the boss was probably used for courtship, as a display structure or for shoving matches between competing males. Among the ceratopsids, this dinosaur is classified in the subfamily Centrosaurinae, representing the largest known member of said lineage. It’s also the namesake of its most derived group, the Pachyrhinosaurini. This creature probably had to contend with large tyrannosaurid predators like Albertosaurus or Nanuqsaurus.