Pachyrhinosaurus

Pachyrhinosaurus Temporal range: Campanian to Maastrichtian, 73.5–69 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
P. lakustai composite skeleton, Royal Tyrrell Museum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Neornithischia
Clade:	†Ceratopsia
Family:	†Ceratopsidae
Subfamily:	†Centrosaurinae
Tribe:	†Pachyrhinosaurini
Clade:	†Pachyrostra
Genus:	†Pachyrhinosaurus Sternberg, 1950
Type species
†Pachyrhinosaurus canadensis Sternberg, 1950
Other species
†P. lakustai Currie, Langston & Tanke, 2008 †P. perotorum Fiorillo & Tykoski, 2012

Pachyrhinosaurus (meaning in Greek "thick-nosed lizard", from Παχυ (pachy), thick; ρινό (rinó), nose; and σαυρος (sauros), lizard)^[1] is an extinct genus of centrosaurine ceratopsid dinosaur from the Late Cretaceous period of North America. The first examples were discovered by Charles M. Sternberg in Alberta, Canada, in 1946, and named in 1950. Over a dozen partial skulls and a large assortment of other fossils from various species have been found in Alberta and Alaska. A great number were not available for study until the 1980s, resulting in a relatively recent increase of interest in Pachyrhinosaurus.

Three species have been identified. P. lakustai, from the Wapiti Formation, the bonebed horizon of which is roughly equivalent age to the upper Bearpaw and lower Horseshoe Canyon Formations, is known to have existed from about 73.5–72.5 million years ago. P. canadensis is younger, known from the lower Horseshoe Canyon Formation, about 71.5–71 Ma ago^[2] and the St. Mary River Formation. Fossils of the youngest species, P. perotorum, have been recovered from the Prince Creek Formation of Alaska, and date to 70–69 Ma ago.^[3] The presence of three known species makes this genus the most speciose among the centrosaurines.