Chasmosaurus: Beast of the Week

Chasmosaurus was a ceratopsian (beaks, horns, and frills) dinosaur that lived in what is now Canada, during the Late Cretaceous Period, between 76.5 and 75.5 million years ago.  From snout to tail it measured about sixteen feet long, and it would have eaten plants when alive.  The genus name, Chasmosaurus, translates to "Chasm Lizard/Dinosaur" in reference to the two large holes, called fenestrae, in its large frill.  These fenestrae are present in the frills of most ceratopsians but are particularly large in Chasmosaurus.

Chasmosaurus russelli life reconstruction by Christopher DiPiazza.

In general, Chasmosaurus had three horns on its face, two relatively narrow ones on the brows, and a robust one on the snout.  The frill was extremely long, and somewhat rectangular.  The genus, Chasmosaurus, has accumulated several species within the genus by paleontologists over the years, but some of those, like Vagaceratops, for example, have since been studied further and given their own genus.  Currently there are two official species of Chasmosaurus.  The older of the two is called Chasmosaurus russelli, which had slightly longer brow horns.  The younger of the two is called Chasmosaurus belli, which had smaller brow horns and a deeper, shallow "V" shape to the center of its frill.

Chasmosaurus belli skeleton on display at the Academy of Natural Sciences in Pennsylvania.

The exact function of the frill is somewhat of a mystery.  At first it could be assumed this was a defensive structure against predators, but it was extremely lightweight and the two holes taking up most of its space don't exactly make it a good shield.  (Although the awkward shape could have still made it difficult for predators to bite the neck.)   The second idea is that the frill helped Chasmosaurus thermoregulate, much like the large ears on many mammals do, by pumping blood through it, cooling it off and thus, the rest of the body.  The third idea for the frill is display.  These frills could have served as devices for communication between members of the same species, whether it be species recognition or for attracting mates.  Although there is no sign of males and females having had differently shaped frills, they may have been different colors in life.

There has been skin impressions found from Chasmosaurus' hip region, showing mosaic-like scales of varying sizes, consisting of larger scales, surrounded by smaller ones, forming patterns.  The preserved skin of Triceratops which was found much more recently is extremely similar.  You may see many artists depicting large ceratopsians like Chasmosaurus or Triceratops with long, quill-like structures growing from these scales, but there is no evidence of this and judging by the actual fossils. (although quill-like scale structures did exist on at least certain older relatives of these ceratopsians, like Psittacosaurus, according to fossil evidence.  More on that another time.)

Photograph of fossilized Chasmosaurus skin.

There was also a wonderfully preserved Chasmosaurus baby that was discovered a few years ago.  This almost complete skeleton, missing only the front limbs, measures about five feet long from beak to tail.  The frill is proportionally shorter which is what we have seen so far with other baby ceratopsians on the fossil record, and the legs aren't proportionally long, as is the case with some other species of baby animals.

Baby Chasmosaurus specimen at the University of Alberta.  Photo courtesy of Darren Tanke.  This specimen is usually seen from the side view.  Note how from this angle you can see that even at this early age, Chasmosaurus had finestre in their frills.

That is all for this week!  Feel free to comment below or on our facebook page.

References

Campbell, J.A., Ryan, M.J., Holmes, R.B., and Schröder-Adams, C.J. (2016). A Re-Evaluation of the chasmosaurine ceratopsid genus Chasmosaurus (Dinosauria: Ornithischia) from the Upper Cretaceous (Campanian) Dinosaur Park Formation of Western Canada.

Dodson, Peter et al. "Chasmosaurus". The Age of Dinosaurs. Publications International. pp. 110–111.

Lull, R.S., 1933, A revision of the Ceratopsia or horned dinosaurs. Memoirs of the Peabody Museum of Natural History 3(3): 1-175

Maidment, S.C.R., and Barrett, P.M., 2011, "A new specimen of Chasmosaurus belli (Ornithischia: Ceratopsidae), a revision of the genus, and the utility of postcrania in the taxonomy and systematics of ceratopsid dinosaur", Zootaxa, 2963: 1-47

Ryan, M.J. & Evans, D.C. (2005). "Ornithischian dinosaurs". Dinosaur Provincial Park: A Spectacular Ecosystem Revealed. In: Currie, P.J. & Koppelhus, E.B. (Eds) Indiana University Press, Bloomington. pp. 312–348.