Pachyrhinosaurus (meaning “Thick-Nosed Lizard”) is a genus of centrosaurine dinosaur to the tribe pachyrhinosaurini and clade pachyrostra from the Late Cretaceous of Canada and the US. The type species was described in 1950 as Pachyrhinosaurus canadensis, described by Charles Sternberg.
In 2008, a second species, P. lakustai, was described by Currie, Langston, and Tanke. The third and most recent species was described in 2012 by Anthony R. Fiorillo and Ronald S. Tykoski, named P. perotorum.
There is also one more species that has yet to be named. The largest species grew to about 26 feet (8 metres) long, while the shortest grew to 18 feet (5.5 metres) long. It had a flat boney structure above most of it’s snout and nose. Some scientists believe that it was like this in life, while others believe that a sharp horn was supported by this structure, called a boss. The closely related Achelousaurus also sported a smaller boss over it’s nose and one over each eye.