Chasmosaurus (Cleft lizard)

Short Info

Chasmosaurus (Cleft lizard)

Phonetic : Kazz-moe-sore-us.

Named By : Lawrence Lambe – 1914

Diet : Herbivore

Size : Estimated 4-5 meters long

Type of Dinosaur : Ceratopsian

Type Species : C. belli (type), C. russelli

Found in : Canada, Alberta – Dinosaur Park Formation

When it Lived : Late Cretaceous, 76-74 million years ago

Chasmosaurus (/,kaezmoU’so:r@sKAZ-mo SAWR-@s) is one of the genus in the ceratopsid dinosaurs that was discovered in the Upper Cretaceous Period of North America. Its name is derived from the word “opening lizard,” referring to the wide gaps (fenestrae) inside its frill (Greek chasma , which means “opening” or “hollow” or ‘gulf’ as well as sauros meaning lizard). Its length was 4.3-4.8 meters (14.1-15.7 feet) and the mass between 1.5-2 tons (1.7-2.2 shorter tonnes), Chasmosaurus was a ceratopsian with a size of average. As with all ceratopsians the species was strictly herbivore. It was originally named Protorosaurus however, this name was previously used for a different animal. The majority of the specimens of Chasmosaurus were taken at the Dinosaur Park Formation of the Dinosaur Provincial Park of Alberta, Canada. The specimens that are referred to as C. russelli originate from the lower part of the formation whereas C. belli comes from the middle and upper beds.

ChasmosaurusROMEduard Solà, CC BY-SA 3.0, via Wikimedia Commons

The year was 1898. Lawrence Morris Lambe of the Geological Survey of Canada made at Berry Creek the first discovery of Chasmosaurus remains in the form of holotype NMC 491, which was a bone from the parietal region that was part of the neck frill. While recognizing that the find was a new species Lambe believed it could be placed within an earlier-discovered genus of ceratopsian short-frilled: Monoclonius. He created this novel type Monoclonius belli to explain his discoveries. The exact name honors the collector Walter Bell.

However, in 1913 Charles Hazelius Sternberg and his sons discovered several completely “M. belli” skulls within the mid Dinosaur Park Formation of Alberta, Canada. Based on their findings, Lambe (1914) erected Protorosaurus (“before Torosaurus”) however the name was taken up with the Permian reptile Protorosaurus and he later invented the new term Chasmosaurus at the beginning of February, 1914. The name Chasmosaurus originates from the Greek the words khasma, Khasma “opening” or “divide” and is used to refer to the large parietal fenestrae found within the frill of skull. Lambe has been is assigned a paratype, the specimen NMC 2245, which was discovered at the Sternbergs in 1913, and comprised of a mostly complete skull with skin impressions.

Since then there have been more remains of skulls and other remains have been discovered that have been classified as Chasmosaurus and a variety of other species have been designated within the Genus. These are believed to be merely an morphological difference in the samples that comprises Chasmosaurus belli skulls, while others are considered to be legitimate varieties of Chasmosaurus or as distinct genera. In 1933, Barnum Brown was credited with the name Chasmosaurus kaiseni to honor Peter Kaisen and based on skull AMNH 5401. It differs in comparison to C. belli by having a brow horn that is very long. This species may be closely related with Chasmosaurus canadensis (‘from Canada’) was named by Thomas M. Lehman in 1990. The species that was originally Monoclonius canadensis Lambe 1902, was classified in the form of Eoceratops canadensis, by Lambe on 19th May 1915. Eoceratops as well as Long-horned Chasmosaurus kaiseni were believed to be examples from Mojoceratops in the work of Nicholas Longrich, although different research teams have discovered Mojoceratops to be an equivalence for Chasmosaurus russelli. Campbell and coworkers, in their analysis of Chasmosaurus specimens, discovered Eoceratops as well as C. kaiseni to be related to Chasmosaurus sp. because of the absence of the parietal in the Holotypes of both. Richard Swann Lull in 1933 identified an unusual, short-muzzled skull as specimen ROM 839 (earlier ROM 5436) found in 1926 as Chasmosaurus brevirostris “with a short snout”. It was thought to be an intermediate synonym for C. belli.

Royal Tyrell Chasmosaurus russelliSebastian Bergmann from Siegburg, Germany, CC BY-SA 2.0, via Wikimedia Commons

Charles Mortram Sternberg added Chasmosaurus russelli in the year 1940, inspired by the specimen NMC 8800 found in the southwestern part of Alberta (lower Dinosaur Park Formation). The name is a tribute to Loris Shano Russell. in 1987 Gregory S. Paul changed the name of Pentaceratops sternbergii to Chasmosaurus sternbergi however it hasn’t received any acceptance. The year 2000 saw George Olshevsky renamed Monoclonius Recurvicornis Cope 1889 to Chasmosaurus Recurvicornis, stating that its fossil material is most likely Chasmosaurine. This is an unofficial nomen dubium.

Chasmosaurus kaiseniRyan Somma, CC BY-SA 2.0, via Wikimedia Commons

Thomas Lehman described Chasmosaurus mariscalensis in 1989, a species from Texas and has since changed its name to Agujaceratops.

The species that was most recently identified is Chasmosaurus Irvinensis, which was identified in 2001. It is a result of the bed at the top that comprise the Dinosaur Park Formation. The species was granted its own name, Vagaceratops, in 2010. However, Campbell et al. (2019) identified Vagaceratops all the way back to Chasmosaurus. In the event that Fowler and Fowler discovered Vagaceratops most likely to represent the sister taxon to Kosmoceratops at the time of 2020 suggested that it should be kept as a distinct genus , separate from Chasmosaurus since its location could be unclear until the chasmosaurines are more fully understood.

Its species Mojoceratops perifania was named after the the holotype specimen TMP 1983.25.1 comprising an incomplete skull, including the parietal as well as from the paratypes TMP 1999.55.292 and an isolated lateral ramus from an right parietal and NMC 8803, the central bar and lateral rami from parietals. There were three specimens AMNH 5656 and NMC 34832 as well as TMP 1979.11.147 as well as (tentatively) AMNH 5401 and NMC 1254 were also assigned to the Genus. The majority of specimens belonging to Mojoceratops were taken out of the Dinosaur Park Formation (late Campanian, 76.5-75 ma) of the Belly River Group of Alberta and Saskatchewan western Canada. Mojoceratops was identified after Nicholas R. Longrich in 2010. The species that is the most common has been identified as Mojoceratops perifania. The generic name comes from mojo. The specific name is “conspicuous pride” in Greek as well as referring to the frill of the skull. It is believed to be based upon fossils that are believed by other researchers to be related to Chasmosaurus.

It is believed that the species Chasmosaurus kaiseni was discovered in sample AMNH 5401, which is a nearly fully (but partly restored) skull that is on display in the American Museum of Natural History it was thought to have characteristics with Mojoceratops perifania and , therefore, was thought to be to be a possible synonym. However the parietal (back edge of the frill) isn’t preserved, and was reconstructed using plaster, based on the remains of Chasmosaurus that led to confusion among scientists during previous years, since the parietal bone is crucial in determining the differences between species of ceratopsids such as Chasmosaurus as well as Mojoceratops. Chasmosaurus kaiseni was later by Longrich considered to be a nomen dubium rather than as the most senior name for M. perifania. Longrich also considered the Holotype of Eoceratops as a possible illustration of Mojoceratops. He thought it was too poorly preserved for an accurate assessment, particularly as it was the younger person. He also regarded to be a nomen dubium rather than the more senior counterpart for M. perifania. A review of 2016 on Chasmosaurus discovered C. kaiseni and Eoceratops to be a reference to Chasmosaurus sp. because of the absence of the parietal preserved within the Holotypes of both.

After the initial assigning of the holotype as well as various skulls belonging to Mojoceratops and other skulls, several research teams published papers in which they questioned the legitimacy of this new Genus. in 2011, Maidment & Barrett failed to prove the existence of any of the supposedly unique characteristics and suggested the possibility that Mojoceratops perifania could be a synonym for Chasmosaurus russelli. Campbell and coworkers, during their study of Chasmosaurus specimens, echoed the findings from Maidment & Barrett, adding that certain supposedly unique characteristics like grooves on the parietal bone found in the Holotype that belongs to C. russelli and, to different levels and in different Chasmosaurus specimens. This variation, they claimed strongly suggests that Mojoceratops was simply a maturing level in the development of C. russelli. Recently, the connection of Eoceratops C. kaiseni, and Mojoceratops to C. russelli was considered not to be true, since the holotype for C. russelli is actually of an upper Dinosaur Park Formation, according to fieldwork conducted recently. This is made more difficult because C. russelli might not be part of the species Chasmosaurus which shares characteristics with the chasmosaurine derived contemporaneously Utahceratops.

The taxonomy of Chasmosaurus is in flux. Based on the above reasons it is possible to be that Mojoceratops, Eoceratops, and C. kaiseni belong to an entirely distinct species, but not genus of chasmosaurine. The specimens identified as C. russelli are all of C. russelli’s Lower Dinosaur Park Formation, stratigraphically and morphologically different from C. belli. Beyond the paratype and holotype extra specimens belonging to C. belli are recognized. This includes AMNH 5422 The ROM-843 (earlier the ROM5499) along with NHMUK’s R4948. all (partial) skull skeletons. Skull YPM 2016,, as well as AMNH 5402, the skeleton and skull 5402 were cited by Campbell and colleagues. (2016) as distinct with other C. belli-related specimens due to having larger epiparietals. The authors considered them to be an individual variations, however the interpretation was rethought after Campbell and co. (2019) identified these specimens as an unknown Chasmosaurus species closely connected to Vagaceratops. The specimen CMN 2245 was linked to as the Vagaceratops-like Chasmosaurus species by Fowler and Freedman Fowler (2020), who wrote in their report that “given the similarity between these two specimens (YPM 2016 and AMNH 5402) and CMN 2245, it is not clear why CMN 2245 was left in C. belli.”

in 2015 Nicholas Longrich presented a new theory that suggests C. belli and C. russelli are synonymous, and a portion of the split remains attributable to the latter as an entirely new species, C. priscus. The paper did not undergo peer review, C. “priscus” is still a name that has no meaning.

Chasmosaurus was a medium-sized cetopsid. In 2010 G.S. Paul calculated the height of C. belli to be 4.8 metresand the weight of two tonnes. C. russelli’s lower Dinosaur Park Formation species would be 4.3 meters long and weigh 1.5 tonnes. The differences that are known in the two forms mostly focus on the horns and frill design, and the postcranias that are referred to as C. russelli are poorly recognized. As with the majority of ceratopsians, Chasmosaurus had three principal facial horns: two on each nostril, and one on each brow. Both species’ horns are rather short, however, in those of the Dinosaur Park species they are slightly larger, particularly the brow horns and more curving backwards. Its frill Chasmosaurus is elongated and wider towards the rear than the front. It’s barely elevated from the snout’s plane. In C. belli, the frill’s rear is V-shaped while its edges are flat. For one of the other DPF species, the back edge is formed in a shallow U while the sides appear convex. The sides were embellished with the skin’s six to nine smaller Ossifications (called episquamosals) or osteoderms, that were attached with the bone squamosale. The frill’s corner had two large osteoderms that were located that were located on parietal bones. The lower DPF species, the outer was the largest and C. belli the middle one. The rest portion of the edge at the rear was devoid of osteoderms. The parietal bones on the frill were punctured with large holes, following which the genus namedthe parietal bone fenestrae. They weren’t like the ovals that are found with the majority of their cousins, but were triangular with one of the points pointing towards the frill’s corner.

Postcranial tissue of C. belli can be preserved best in the specimen dubbed NHMUK 4948. The three cervical vertebrae that are the first are joined to form a syncervical unit like other neoceratopsians. There are five additional cervicals that are preserved in this specimen to make a total of 8 that could be the complete neck. The cervicals from four to eight are amphiplatian, larger than long and nearly identical in length. Dorsal vertebrae are amphiplatian. C. belli was an synsacrum which was an equilateral unit that consists of dorsal, sacral, and sometimes caudal vertebrae dependent on the specimen.

The Chasmosaurus specimen NMC 2245, discovered by C.M. Sternberg was supported by skin impressions. The preserved area, which was located in left hip to right was about one by 0.5 meters. The skin been covered with large scales, which were well-spaced horizontal rows within smaller scales. The larger scales were of an area of as large as fifty millimetres. They were also separated from one another by 5-10 centimetres. They were either hexagonal or pentagonal and had the possibility of having five to six sides. Each side had smaller scales that were making an Rosette. Small, non-overlapping, convex scales measuring around 1 centimetre in size surrounded the entire. The larger scales wrinkled because of straight grooves that were oriented in a perpendicular direction to their borders. Between the top and bottom the scales with large rows diminuted in the size. Unfortunately, little can yet be discovered about hue of Chasmosaurus from the fossilized skin impressions.

Source: Wikipedia