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]
Chasmosaurus may have defended their young by forming a protective circle, turning their horns toward the predator.
Description[]
Size comparison of several members of Ceratopsidae with a human, Chasmosaurus in green
Chasmosaurus was a medium-size ceratopid. In 2010 G.S. Paul estimated the length of C. belli at 4.8 metres, its weight at two tonnes; C. russelli would have been 4.3 metres long and weighed 1.5 tonnes.
Restoration of C. belli
The known differences between the two species mainly pertain to the horn and frill shape, as the postcrania of C. russelli are poorly known. Like many ceratopsians, Chasmosaurus had three main facial horns - one on the nose and two on the brow. In both species these horns are quite short, but with C. russelli they are somewhat longer, especially the brow horns, and more curved backwards. The frill of Chasmosaurus is very elongated and broader at the rear than at the front. It is hardly elevated from the plane of the snout. With C. belli the rear of the frill is V-shaped and its sides are straight. With C. russelli the rear edge is shaped as a shallow U, and the sides are more convex. The sides were adorned by six to nine smaller skin ossifications (called episquamosals) or osteoderms, which attached to the squamosal bone. The corner of the frill featured two larger osteoderms on the parietal bone. With C. russelli the outer one was the largest, with C. belli the inner one. The remainder of the rear edge lacked osteoderms. The parietal bones of the frill were pierced by very large openings, after which the genus was named: the parietal fenestrae. These were not oval in shape, as with most relatives, but triangular, with one point orientated towards the frill corner.
Replica of skin impressions
Interestingly, a Chasmosaurus NMC 2245 specimen recovered by C.M. Sternberg was accompanied by fossilized skin. The area conserved, from the right hip region, measured about one by 0.5 metres. 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[]
Skull of Chasmosaurus belli, Canadian Museum of Nature
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]
Skull of Chasmosaurus russelli, Royal Tyrell Museum of Palaeontology.
Stratigraphic positions of chasmosaurine specimens from the Dinosaur Park Formation
Discoveries and species[]
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George F. Sternberg preparing a C. belli skull in 1914
In 1898, Lawrence M. Lambe of the Geological Survey of Canada made at the Berry Creek the first discovery of Chasmosaurus remains, holotype NMC 491, a parietal bone that was part of a neck frill. Although recognizing that his find represented a new species, Lambe thought this could be placed in a previously-known short-frilled ceratopsian genus: Monoclonius. He erected the new species Monoclonius belli to describe his finding.[4] The specific name honoured collector Walter Bell.
But, in 1913, Charles Sternberg and his sons found lots of full "M. belli" skulls in the middle Dinosaur Park Formation of Alberta, Canada. In January 1914, Lambe named all these finds as a separate genus: Protorosaurus, the name indicating an ancestry to Torosaurus. However, this name quickly was shown to be preoccupied by a Permian reptile, Protorosaurus Meyer 1836. Therefore Lambe created the replacement name Chasmosaurus in February 1914. It is derived from Greek χάσμα, khasma, "opening" or "divide" and refers to the very large parietal fenestrae in the skull frill. Lambe now also assigned a paratype, specimen NMC 2245 found by the Sternbergs in 1913 and consisting of a largely complete skeleton, including skin impressions..[4]
C. russelli, Royal Tyrrell Museum
Since then, more Chasmosaurus remains, including skulls, have been found. There seems to be morphological variation from the known sample of Chasmosaurus skulls,[5] Today some of these are considered to only reflect a morphological variation among the known sample of Chasmosaurus belli skulls; others are seen as valid species of Chasmosaurus or as separate genera. In 1933 Barnum Brown named Chasmosaurus kaiseni, honouring Peter Kaisen and based on skull AMNH 5401, differing from C. belli in having very long brow horns. This form is perhaps related to Chasmosaurus canadensis ('from Canada') named by Thomas M. Lehman in 1990. The latter species, originally Monoclonius canadensis Lambe 1902, had been described as Eoceratops canadensis by Lambe in 1915. Eoceratops and the long-horned Chasmosaurus kaiseni are for now thought to be examples of Mojoceratops.[6] Richard Swann Lull in 1933 named an unusual, short-muzzled skull, specimen ROM 839 (earlier ROM 5436) collected in 1926, as Chasmosaurus brevirostris, "with a short snout". This has been seen as a junior synonym of C. belli. 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]
Holotype of C. irvinensis at Canadian Museum of Nature
The most recently described species is C. irvinensis, which stems from the top beds of the Dinosaur Park Formation. The specific name honours Loris Shano Russell. This species got its own genus, Vagaceratops, in 2010.[8]
In 1987, Gregory S. Paul renamed Pentaceratops sternbergii into Chasmosaurus sternbergi, but this has found no acceptance. In 2000, George Olshevsky renamed Monoclonius recurvicornis Cope 1889 into Chasmosaurus recurvicornis as its fossil material is likely chasmosaurine; this is a nomen dubium.
Today, only two species are seen as valid: C. belli and C. russelli. They show small differences in morphology and a difference in stratigraphy, as C. russelli is found in the older lower Dinosaur Park Formation and C. belli in the middle Dinosaur Park Formation of the Campanian, together spanning a time period of 76.5 to 75.5 million years ago. Apart from the holotype and paratype several additional specimens of C. belli are known. These include AMNH 5422, AMNH 5402, ROM 843 (earlier ROM 5499) and NHMUK R4948, all (partial) skeletons with skull; and YPM 2016, a skull. Apart from its holotype C. russelli is known from its paratype CMN 8803, a skull frill; CMN 41933, a rear skull frill; RTMP 81.19.175, the right side of a skull and CMN 2280, a partial skeleton with skull found by the Sternbergs in 1914.
Paleobiology[]
Depiction of the mega-herbivores in the Dinosaur Park Formation, C. belli on the left
Chasmosaurus shared its habitat, situated on the east coast of Laramidia, with species of Centrosaurus. Niche partitioning may have occurred, due to Chasmosaurus having elongated snout and jaws, which may mean the animal was selective in food. The horns and frill however, are still unknown in function. The horns are short and recurved and the frills fenestrae are so large they could not have served much defensive purpose. One author argues that the beak was the animals main defense. It is also proposed that the frill could make the animal look larger while thermoregulating. The frill may have even been brightly coloured in acts of sexual display and mating. However this is hard to prove due to Lull suggesting in 1933 that C. kaiseni, a species that bore long horns, was a male C. belli. They also suggested that females bore shorter horns. In 1927 C. M. Sternberg came to the following conclusion: two skeletons of which he mounted in the Canadian Museum of Nature, NMC 2245 and NMC 2280, where of different genders. The first was a smaller male and the second, a larger female. Today, both are listed under different species.
Juvenile; UALVP 52613.
A juvenile specimen if Chasmosaurus belli is known, which shows that the dinosaur may have cared for its young. The specimen is 3 years of age and is 5 feet long. It as similar limb proportions to adults. This means that Chasmosaurus were not fast-moving, and that juveniles did not need to be to keep pace with adults. The specimen was complete, however the front limbs had fallen into a sinkhole before recovering. Skin impressions also appear beneath the specimen, and the matrix shows that the individual may have drowned while crossing a river. Further study shows that the juvenile has a less wide frill in the rear, and the frill is proportionally shorter than in adult skulls, as well.
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.
Appearance in other media[]
Jurassic Park[]
- Chasmosaurus is set to appear in Jurassic World: Evolution as shown in its species profile. Its coloration is mainly reddish-brown with a creamy belly, with a tint of blue in the frill.
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Read more Chasmosaurus on Jurassic Park Wiki |
The Land Before Time[]
- A Chasmosaurus makes a brief appearance fighting two fast biters in Land Before Time III: The Time of Great Giving.
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Read more Chasmosaurus on Land Before Time Wiki |
Links[]
References[]
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- ↑ 4.0 4.1 Dodson, Peter; et al.. "Chasmosaurus". The Age of Dinosaurs. Publications International. pp. 110–111. ISBN 0785304436.
- ↑ 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.
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