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Chasmosaurus

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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.[1]

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,[2] 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.[3]

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.[4]

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.[4]

Since then, more Chasmosaurus remains, including skulls, have been found. There seems to be morphological variation from the known sample of Chasmosaurus skulls,[5] 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.[6] 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).[5] Thomas Lehman described C. mariscalensis in 1989 from Texas, which has now been renamed Agujaceratops.[7] 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.[8]

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.

Chasmosaurus in The Land Before Time

Chasmosaurus only appears briefly in The Land Before Time III: The Time of the Great Giving. In the beginning of the film, a pack of blue Dromaeosauruses attack a Chasmosaurus in the Mysterious Beyond. One of the raptors lunges, and the screen fades into the Great Valley. It is unknown what happens to the Chasmosaurus. Based on this single appearance, Chasmosaurus in the Land Before Time are red with pale underbellies and darker spots inside their frills. It is unknown if the Land Before Time characters consider them Threehorns like Triceratops or if they are known by a different term.

Gallery

References

  1. 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. 
  2. Dodson, Peter; et al.. "Chasmosaurus". The Age of Dinosaurs. Publications International. pp. 110–111. ISBN 0785304436. 
  3. 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. 
  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. Nicholas R. Longrich (2010). "Mojoceratops perifania, A New Chasmosaurine Ceratopsid from the Late Campanian of Western Canada". Journal of Paleontology 84 (4): 681–694. doi:10.1666/09-114.1. 
  7. Lucas SG, Sullivan RM, Hunt AP (2006). "Re-evaluation of Pentaceratops and Chasmosaurus (Ornithischia: Ceratopsidae) in the Upper Cretaceous of the Western Interior". New Mex Mus. Nat. Hist. Sci. Bull. 35: 367–370. 
  8. Scott D. Sampson, Mark A. Loewen, Andrew A. Farke, Eric M. Roberts, Catherine A. Forster, Joshua A. Smith, Alan L. Titus (2010). "New Horned Dinosaurs from Utah Provide Evidence for Intracontinental Dinosaur Endemism". PLoS ONE 5 (9): e12292. doi:10.1371/journal.pone.0012292. PMID 20877459. PMC: 2929175. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0012292. 

External links

Walking the Chasmosaur, a 3D Dino Movie

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