Pachyrhinosaurus: Prehistoric Beast of the Week

This week belongs to a unique ceratopsian dinosaur, Pachyrhinosaurus!  Pachrhinosaurus was a very successful plant-eater that lived in what is now Canada and Alaska during the Late Cretaceous period.  There are actually three different species within this genus that range in age from 73 million to about 69 million years old.  Pachyrhinosaurus was one of the largest ceratopsians, the biggest individuals measuring over twenty feet long from beak to tail.  The name, Pachyrhinosaurus, translates to "Thick Nose Dinosaur".

Pachyrhinosaurus perotorum life reconstruction in watercolor by Christopher DiPiazza.

While many other ceratopsians had horns growing from their noses and brows, Pachyrhinosaurus had a wide, flat structure called a boss, earning it its genus name.  In addition to this boss, Pachyrhinosaurus of all species had horns growing out of their frills.  Some curved outwards, while others curved more dramatically downwards.  There is even a decent amount of variation among horn shape and length among adults of the same species.  This could be due to age or even sex.  Further more, according to the baby Pachyrhinosaurus skulls on the fossil record, we know they didn't have any of this dramatic headgear until much later in life, so it may have been a sexual display adaptation, or possibly for fighting fellow adults for dominance.

Pachyrhinosaurus lakustai skull on display at the Royal Belgian Institute of Natural Sciences.

As stated above, Pachyrhinosaurus is known from three different species.  The two Canadian species are called Pachyrhinosaurus canadensis and Pachyrhinosaurus lakustai.  P. lakustai is the oldest, having lived between 74 and 73 million years ago.  P. lakustai was unique in that many specimens had prominent horns growing out of the centers of their frills.  Some refer to it as the "unicorn dinosaur" because of this.  Pachyrhinosaurus canadensis is slightly younger, having lived between 72 and 71 million years ago, with a bigger nose boss.  Finally, there is the youngest species that lived all the way up in what is now Alaska, Pachyrhinosaurus perotorum, which lived between 79 and 69 million years ago, with the overall most extensive nose boss of the three species.  (There is certainly individual variation between specimens of each species. Not every individual P. perotorum had a bigger nose boss than every single P. canadensis, for instance.)

Pachyrhinosaurus is sometimes referred to as having a "unicorn horn".

Pachyrhinosaurus is a well-studied dinosaur, known from many specimens.  In fact, there were over a dozen skeletons of this dinosaur all discovered together in the same area in Alberta, Canada, called Pipestone Creek.  It is possible that the poor dinosaurs died trying to swim across a river that had flooded.  Among these specimens there were small juveniles all the way up to large adult animals.  This tells us that Pachyrhinosaurus was a dinosaur that at least sometimes lived in groups and most likely looked out for its young.

Pachyrhinosaurus canadensis at the Geological Society in Copenhagen.

When alive, Pachyrhinosaurus would have co-existed with many other dinosaurs including Edmontosaurus regalis and the tyrannosaurid, Albertosaurus.  The Alaskan Pachyrhinosaurus perotorum would have probably met Nanuqsaurus, another tyrannosaurid.

Pachyrhinosaurus belongs to a group, or subfamily, called centrosaurinae within the ceratopsian group.  Centrosaurine ceratopsids tended to have taller, thicker snouts, longer tails, and shorter frills than other large ceratopsids.  They also typically (not always) were devoid of long brow horns and instead sported large, bony structures on their snouts.  Other examples of centrosaurine ceratopsians are Styracosaurus and Sinoceratops.

That's all for this week!   Join us next week for the last prehistoric animal review of 2013!  As always feel free to comment below or on our facebook page! 

References

Anthony R. Fiorillo and Ronald S. Tykoski (2012). "A new species of the centrosaurine ceratopsid Pachyrhinosaurus from the North Slope (Prince Creek Formation: Maastrichtian) of Alaska". Acta Palaeontologica Polonica 57 (3): 561–573. doi:10.4202/app.2011.0033.

C. M. Sternberg. 1947. New dinosaur from southern Alberta, representing a new family of the Ceratopsia. Geological Society America Bulletin 58:1230

Currie, P.J., Langston, W., and Tanke, D.H. (2008). "A new species of Pachyrhinosaurus (Dinosauria, Ceratopsidae) from the Upper Cretaceous of Alberta, Canada." pp. 1-108. In: Currie, P.J., Langston, W., and Tanke, D.H. 2008. A New Horned Dinosaur from an Upper Cretaceous Bone Bed in Alberta. NRC Research Press, Ottawa, Ontario, Canada. 144 pp. ISBN 978-0-660-19819-4

E. B. Koppelhus. 2008. Palynology of the Wapiti Formation in the northwestern part of Alberta with special emphasis on a new Pachyrhinosaur bonebed. International Dinosaur Symposium in Fukui 2008: Recent Progress of the Study on Asian Dinosaurs and Paleoenvironments. Fukui Prefectural Dinosaur Museum, Fukui 65-66.