Chasmosaurus

Before formal naming or identification, this organism was known as the following on this wiki:
**Bonhams chasmosaur** and **Auctioned chasmosaur skull**

## Statistics

### Species

*C. belli
C. russelli
C. irvinensis*?

### Synonyms

*Eoceratops*?
*Mojoceratops?
Vegaceratops*?
*Protorosaurus* (preoccupied)
"C. priscus"
*"M." sphenocerus*

### Diet

Herbivorous

*Chasmosaurus* is an extinct genus of chasmosaur that lived in North America during the Late Cretaceous.

## History

Lawrence Lambe (1898) found the holotype of *Chasmosaurus*, NMC 491, at Berry Creek. This consists of a parietal, placed in *Monoclonius*, assigning a new species *M. belli*. It was named after Walter Bell. However, in 1913, Charles Sternberg found several complete skulls from the middle Dinosaur Park Formation. He erected *Protorosaurus* to house these materials, but found it was preoccupied by a Permian reptile. By February of 1914, he erected *Chasmosaurus*. Lambe assigned NMC 2245, a near-complete skeleton with skin impressions, as a paratype. It was found by the Sternbergs in 1913. Since, more specimens, including skulls, were found and assigned to *Chasmosaurus*.

Various species assigned are seen today are morphological variation within *C. belli*, with some fit into other genera and few remain valid. Barnum Brown (1933) named *C. kaiseni* after Peter Kaisen and based on AMNH 5401. It was differentiated based on long brow horns. This may be related to Thomas Lehman's (1990) *C. canadensis*, which had been classified as *Monoclonius* (1902) and *Eoceratops* (1915) by Lambe. *Eoceratops* and *C. kaiseni* were thought to have been exemplars of *Mojoceratops* by Nicholas Longrich, though other teams have found it a synonym of *C. russelli*. Campbell et al. (2016) in an analysis of *Chasmosaurus* specimens found *C. kaiseni* and *Eoceratops* were referable to *C. sp.* due to the lack of parietal preservation. Richard Lull (1933) named *C. brevirostris* based on the short-snouted ROM 839 (previously ROM 5436), which was recovered in 1926. This is a junior synonym of *C. belli*. Charles Sternberg (1940) added *C. russelli* based on NMC 8800. It was named after Luis Shano Russelp and from the lower Dinosaur Park Formation.

Gregory S. Paul (1987) renamed *Pentaceratops sternbergi* into *C. sternbergi*, but this is not openly accepted. George Olshevsky (2000) renamed *Monoclonius recurvicornis* into *C. recurvicornis*, since the material is a likely chasmosaur. It is now seen as a new genus. Lehman (1989) named *C. mariscalensis*, which was given the genus *Agujaceratops*. *C. Irvinensis* is the most recently described, from the uppermost Dinosaur Park beds in 2001. In 2010, it was assigned *Vagaceratops*. Campbell et al. (2019), however, synonymized it with *Chasmosaurus*. Fowler and Fowler found *Vagaceratops* was sister to *Kosmoceratops* in 2020, suggesting it was distinct since it would have unstable placement until *Chasmosaurus* are better understood.

*Mojoceratops perifania*, based on holotype TMP 1983.25.1 (a partial skull with parietal) and paratpes TMP 1999.55.292 (an isolated lateral ramus of the right parietal and NMC 8803 (a central bar with lateral rami). AMNH 5656, NMC 34832 and TMP 1979.11.147 and AMNH 5401 and NMC 1254 were tentatively assigned to the genus. All of these were from the Belly River Group, Dinosaur Park Formation, Alberta and Saskatchewan. They were all once assigned to *Chasmosaurus*, but were reassigned to *Mojoceratops*.

*C. kaiseni*, from AMNH 5401, a near-complete but partially restored skull, was thought to share features with *Mojoceratios* and considered a possible synonym. The parietal is not preserved, and instead restored based on *Chasmosaurus* specimens. *C. kaiseni* was considered by Longrich to be a nomen dubium rather than a senior synonym of *Mojoceratops*. Longrich also considered the *Eoceratops* holotype as a probable exemplar of *Mojoceratops*. However, it was considered too poorly preserved to determinate reliably, which was further made clear by the immaturity of the specimen. A 2016 overview assigned *C. kaiseni* and *Eoceratops* to *Chasmosaurus sp.* due to no preserved parietals.

Several researchers began to investigate the validity of *Mojoceratops*. Maidment and Barrett (2011) failed to find differentiating features, arguing it was a synonym of *C. russelli*. Campbell et al. (2016) agreed with the previous assessment, but found some features, such as grooves in the parietal, to be present in the *C. russelli* holotype other *Chasmosaurus* specimens (to a degree). They argued this variability represents a growth stage of *C. russelli*. The referral of *Eoceratops*. *C. kaiseni* and *Mojoceratops* to *C. russelli* was found doubtful, since the holotype of *C. russelli* is from the upper Dinosaur Park Formation, which was found via recent fieldwork. This is made more complicated by the fact *C. russelli* may not be attributable to *Chasmosaurus*, since it shares features with the contemporaneous *Utahceratops*.

The taxonomy of *Chasmosaurus* constantly changes. It is likely *Mojoceratops*, *Eoceratops* and *C. kaiseni* are a distinct species or genus of chasmosaur. *C. russelli* are from the lower Dinosaur Park, which is stratigraphically and morphologically separate from *C. belli*. Apart from the holotype and paratype, more *C. belli* specimens are known, including AMNH 5422, ROM 843 (previously ROM 5499) and NHMUK R4948, partial skeletons with skulls. YPM 2016 (a skull) and AMNH 5402 (a skeleton) were noted by Campbell et al. (2016) as different from *C. belli* by having more epiparietals, but this was concluded as individual variation. However, Campbell et al. (2019) found these as *Chasmosaurus* indet. closely related to *Vagaceratops*. CMN 2245 was found to be a *Vagaceratops*-like *C. sp.* by Fowler and Frredman Fowler (2020) noting 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."

"C. priscus" was a nomen nudum Nick Longrich coined to refer to *C. russelli* specimens. The paper was submitted, but later declined. David Evans has suggested *"Monoclonius" sphenocerus* is undiagnostic and very similar to *Centrosaurus*.

A skull discovered, collected, prepared and embedded into plaster from the Belly River Formation (=Belly River Group) by Sternberg was out up for auction at Bonhams in 2013 by the San Diego Natural History Museum. Soon after, the museum removed the item for sale but left the *Xiphactinus* and mosasaur specimens that were alongside the skull for sale. The tag identified it as part of this genus.

## Description

*Chasmosaurus* was initially to be named *Protorosaurus*, but was preoccupied by a basal archosauromorph. *C. belli* and *C. russelli* are differentiated by horn and frill morphology, and the postcranial elements of the latter are poorly known, however the horns are slightly longer and more recurved. *Chasmosaurus* frills are extremely elongate and wide in the rear, hardly elevated from the skull. *C. belli* has a V-shaped frill that is straight by the sides. *C. russelli* has a shallow U-shape near the rear and more convex sides. The sides were adorned with 6 to 9 osteoderms which attached to the squamosal. The parietal bones feature two large osteoderms. *Russelli*'s outer is larger and *belli*'s inner is larger. The rear edge lacks osteoderms altogether. Each parietal is covered in massive openings, of which the genus is named from. They are not oval shaped, but triangular, one point facing the frills corner.

Postcranials are known from a single specimen, NMC 2245 which was recovered by C. M. Sternberg and contains skin impressions. The impressions are from the right hip, and spans 0.5 meters. Large scales sit in rows with smaller scales between. Large scales reach up to 55 millimeters in diameter, and distance from one-another 5-10 millimeters. They are pentagonal or hexagonal. Each touches a smaller scale which forms a rosette. Small non-overlapping convex scales about 1 centimeter surrounds each. Larger scales wrinkle due to straight indents arranged perpendicular to their edges. From the top to the bottom of the impressions, large scales become less populated near the underside of the creature. However, no colour patterns traces are preserved, so nothing of the animals colour is currently known.

## Paleobiology

*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.

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.

## Species

### Reassigned Species

* *"C." mariscalensis*
* *"C." gettyi*
* *"C." sternbergii*

## References

* https://en.wikipedia.org/wiki/Chasmosaurus
* https://f1000research.com/articles/4-1468
* https://twitter.com/DavidEvans\_ROM/status/1352663438330388486
* https://twitter.com/DavidEvans\_ROM/status/1352672974944534530
* https://archive.org/details/g.s.paul2016theprincetonfieldguidetodinosaurs/page/n258/mode/1up
* https://www.nationalgeographic.com/science/article/historical-fossils-may-be-lost-at-auction
* https://www.bonhams.com/auctions/21076/lot/1004/