Chasmosaurus

*Chasmosaurus belli*

* Timothy Bradley Artwork
* Robert F Walters Artwork

**Chasmosaurus** was a ceratopsian dinosaur from Canada in the Cretaceous. Its name means 'opening lizard', referring to the large openings in its frill (Greek *chasma* meaning 'opening' or 'hollow' or 'gulf' and *sauros* meaning 'lizard'). With a length of 16–20 ft and a weight of 4 short tons, *Chasmosaurus* was a ceratopsian of average size. Like all ceratopsians, it ate plants. At first it was to be called *Protorosaurus*, but this name had been previously published for another animal. All specimens of *Chasmosaurus* were collected from the Dinosaur Park Formation of the Dinosaur Provincial Park of Alberta. *C. russelli* comes from the lower beds of the formation while *C. belli* comes from middle and upper beds.

## Description

The frill of *Chasmosaurus* has been described as "heart-shaped", since its bone structure is made up of two large 'loops' from a core bone.

Some finds have a few small bones, which may have grown from the edge of the frill. The frill may have been brightly colored too, to draw attention to its size or as part of mating display. But, the frill was so large and yet so weak (since most of it was skin stretched between the bones) that it could not have provided much functional defense. It may have just used to seem massive or control for temperature.
Like most ceratopsians, chasmosaurs had three main horns on their face - one on the nose and two on the brow. Different fossil finds have produced vague results - one species of *Chasmosaurus*, named *C. kaiseni*, bore long brow horns, while *C. belli* had only short ones. While these were at first named as different species, it now seems that the long horns may have come from males and the short horns from females.

Interestingly, a *Chasmosaurus* specimen recovered by Sternberg was accompanied by fossilized skin.The skin seems to have had lots of large scales in evenly spaced rows among smaller scales, with five or six sides per knob. Sad to say, not a thing can be learned of the color of *Chasmosaurus* from the known fossil skin samples.

## Classification

Ceratopsians are split into two subfamilies by taxonomists; those with short frills (centrosaurines), such as *Centrosaurus* and those with long frills (chasmosaurines), of which *Chasmosaurus* was one. As well as the larger frill, the long-frilled ceratopsians typically had longer faces and jaws and some paleontologists think that they were more selective with the plants they ate. Long frills were a relatively late development in dinosaur evolution, since even *Chasmosaurus* dates from the late Cretaceous Period, 76.5 to 75.5 million years ago.

## Discoveries and species

In 1898, Lawrence M. Lambe of the Geological Survey of Canada found the first *Chasmosaurus* remains- part of a neck frill. While he knew that his find formed a new species, Lambe thought it was from a *Monoclonius*. He built the new species *Monoclonius belli* to describe it.

But, in 1913, Charles Sternberg and his sons found lots of full "M. belli" skulls in the middle Dinosaur Park Formation of Alberta, Canada.These were finally described as the new genus *Chasmosaurus* in 1914, once more by Lawrence Lambe.

Since then, more *Chasmosaurus* remains, including skulls, have been found. There seems to be morphological variation from the known sample of *Chasmosaurus* skulls, so there are a few known species of *Chasmosaurus*. Lambe's original *C. belli* ('Bell's cleft lizard') was joined by *C. canadensis* ('from Canada') in the same year. The latter species had been described as *Eoceratops canadensis* by Lambe but was later reclassified as a chasmosaur by Thomas M. Lehman. *Eoceratops* and the long-horned *Chasmosaurus kaiseni* are for now thought to be examples of *Mojoceratops*. Lull named a strange, short-muzzled skull, collected in 1926, *C. brevirostris*. C. M. Sternberg added *C. russelli*, in 1940, from Alberta (Dinosaur Park Formation). Thomas Lehman described *C. mariscalensis* in 1989 from Texas, which has now been renamed *Agujaceratops*. The most recently described species is *C. irvinensis*, which stems from the top beds of the Dinosaur Park Formation. This species got its own genus, *Vagaceratops*, in 2010.

## Paleobiology

The fact that the bones of several individuals were found grouped in some sites in Alberta suggests that they lived in herds. Some of the sites came to contain remains of tens or even hundreds of individuals. The sites of bones were formed very fast due to some catastrophic event, like the eruption of a volcano. But some research has specified that it was the overflow of a river, which suggest that a whole herd was killed trying to cross the river by swimming. In case a herd was attacked by a predator, such as *Tyrannosaurus*, males could have formed a ring and, with all the frills facing out, would have presented a formidable sight. Chasmosaurus deposits can make us understand that horned dinosaurs migrated through distances too, although this idea is hard to pass. Currently, herds of wildebeest have to cross many rivers, where many individuals die.

## JPInstitute.com Description

Chasmosaurus was the oldest of the long-frilled, horned ceratopsian dinosaurs, whose family includes Triceratops. It was a medium-sized plant-eater that had a long neck frill with large holes in the bone and narrow structures to support the weight of the frill. It would have had skin stretched over the holes in its frill. Chasmosaurus had medium-sized horns over its eyes, and a smaller nose horn.

Judging from the monotypic bone beds of the Chasmosaurus fossils, this animal traveled in single species herds. Since the frill of a Chasmosaurus would not be a very effective defensive weapon, there is speculation that it may have been used for identification and attracting mates. New discoveries suggest the possibility that Chasmosaurus and Pentaceratops might belong in the same genus.

## Links

http://web.archive.org/web/20040214154750/http://www.jpinstitute.com/dinopedia/dinocards/dc\_chasm.html

## References

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4. ↑ 4.0 4.1 Dodson, Peter; *et al.*. "Chasmosaurus". *The Age of Dinosaurs*. Publications International. pp. 110–111. ISBN 0785304436.
5. ↑ 5.0 5.1 Arbour, V. M.; Burns, M. E.; and Sissons, R. L. (2009). "A redescription of the ankylosaurid dinosaur *Dyoplosaurus acutosquameus* Parks, 1924 (Ornithischia: Ankylosauria) and a revision of the genus". *Journal of Vertebrate Paleontology* **29** (4): 1117–1135. doi:10.1671/039.029.0405.
6. ↑ Template:Cite journal
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