Kosmoceratops
Kosmoceratops | |
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Skull cast with reconstructed predentary bone, right horn, and left part of face | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | †Ornithischia |
Clade: | †Ceratopsia |
Family: | †Ceratopsidae |
Subfamily: | †Chasmosaurinae |
Genus: | †Kosmoceratops Sampson et al., 2010 |
Species: | †K. richardsoni
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Binomial name | |
†Kosmoceratops richardsoni Sampson et al., 2010
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Kosmoceratops (
Kosmoceratops had an estimated length of 4.5 m (15 ft) and a weight of 1.2 t (1.3 short tons). As a ceratopsid, it would have been
Studies of bone
Discovery
Since 2000, the
In 2010, the paleontologist
The describers of Kosmoceratops named the new chasmosaurine genera
In 2017, the US government announced plans to shrink the GSENM (to little over half its size) and Bears Ears monuments to enable coal mining and other energy development on the land, which was the largest reduction of US national monuments in history.[10][11] Sampson, who had overseen much of the early research at the former monument, expressed fear that such a move would threaten further discoveries. Media outlets stressed the importance of the area's fossil discoveries—including more than 25 new taxa—while some highlighted Kosmoceratops as one of the more significant finds.[11][12][13][14] The US government was subsequently sued by a group of scientists, environmentalists, and Native Americans; in 2021, the monument was restored to its former extent by the new administration.[10][13][15]
A partial skull (cataloged as CMN 8801) discovered in 1928 by fossil collector
Description
Kosmoceratops is estimated to have been 4.5 m (15 ft) long and to have weighed 1.2 t (1.3 short tons). As a ceratopsid, it would have been a
The region around the
The parietosquamosal neck frill (formed by the parietal and squamosal bones) of Kosmoceratops was very
The epiossifications on the squamosal bones of Kosmoceratops became progressively larger towards the back of the neck frill. There were five well-developed epiossifications per side on the hind-margin of the frill: three forward-curved epiparietals (ep 1–3) on the parietal bone, one forward-curved epiparietosquamosal (esp) on the border between the parietal and squamosal bones, and one episquamosal (es1) on the squamosal bone that was directed to the side and downward. The forward-curving epiparietals had prominent
The epiossification numbering system presented above follows that used by Sampson and colleagues in 2010, but note that Fowler and Fowler proposed an alternate system in 2020, based on comparison with earlier Chasmosaurus species. Following this system, epiparietals 1-3 of Kosmoceratops were collectively a single, sideways expanded ep1, the epiparietosquamosal became epiparietal 2, and the episquamosal was epiparietal 3. The epiossification numbers of Vagaceratops were similarly revised.[2][20]
Classification
Two
In 2011 and 2014, Longrich found the sole species of Vagaceratops to be retained in Chasmosaurus, where it had been placed originally (as C. irvinensis), while Kosmoceratops did not cluster closely with other taxa.
In a 2011 conference abstract, the paleontologist Denver W. Fowler and colleagues suggested that many ceratopsid genera were merely ontogenetic morphs (or growth stages) of other genera and that Kosmoceratops was an immature stage of C. irvinensis (with the prominent skull ornamentation reducing with age).
In 2016, Mallon and colleagues found Kosmoceratops and Vagaceratops to form a clade, with the new genus Spiclypeus as sister taxon. While they acknowledged that some researchers had grouped Vagaceratops with Chasmosaurus instead, they found the forward-curled epiossifications at the back of the frill very distinctive, suggesting that Spiclypeus provided clues to explain the evolution of this feature. They suggested that the curving of these epiossifications occurred stepwise on the lineage leading to Kosmoceratops, those in the middle curling first, followed by those at the sides. This process would have occurred before the shortening of the frill and constriction of the parietal fenestrae, since these features were in their more "primitive", unaltered condition in Spiclypeus. Despite Spiclypeus being seemingly transitional in these regards, it lived around the same time as Kosmoceratops and therefore could not have been ancestral to it. The cladogram below is based on Mallon and colleagues' 2016 analysis:[29]
Ceratopsidae |
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In 2020, Fowler and Fowler described two new chasmosaurine genera, and suggested the subfamily had a deep evolutionary split between a clade containing Chasmosaurus and its closest relatives, and Pentaceratops and its relatives. Contrary to previous studies and informed by their new epiossification numbering system, Kosmoceratops was found to be closer to Chasmosaurus, and together with Vagaceratops, represented the most derived and youngest members of that lineage. According to this interpretation, Kosmoceratops evolved from Vagaceratops, which evolved from Chasmosaurus. As they found Vagaceratops likely to be the sister taxon of Kosmoceratops, they suggested it should be maintained as a distinct genus from Chasmosaurus, as its placement would probably remain unstable until chasmosaurines are better understood. Spiclypeus was not evaluated in their study, among other recently named chasmosaurines.[20]
Paleobiology
In a 2013 Master's thesis (summarized in a published paper by different authors in 2019
In a 2017 Master's thesis, the paleontologist Nicole Marie Ridgwell described two
Function of skull ornamentation
The possible functions of ceratopsian horns and frills have been debated, including fighting off predators,
In 2013, the paleontologists David E. Hone and Darren Naish criticized the "species recognition hypothesis", arguing that no extant animals use such structures primarily for species recognition and that Padian and Horner had ignored the possibility of mutual sexual selection (where both sexes are ornamented). They noted that if the primary purpose of the structures was species recognition, they would have differed in the shape of a single structure because additional structures would have been redundant at additional cost. Ceratopsians, for example, had elaborate nasal horn, brow horn, jugal boss, frill midline, and frill edge features, as well as differences in body size and proportions, while the absence or presence of a single horn would have been enough to differentiate between sympatric species.[34] In 2018, the paleontologist Andrew Knapp and colleagues examined whether the diverging ornamental traits of ceratopsians were correlated with sympatricity between two or more species, as would be predicted by the "species recognition hypothesis". They found that display patterns diverged widely overall while those of sympatric species did not differ significantly from those of non-sympatric species, concluding that the hypothesis did not have statistical support among ceratopsians.[35]
In 2015, biologist Pasquale Raia and colleagues examined the evolutionary increase in the complexity and size of animal ornaments (such as crests, horns, and tusks) over time, using
Paleoenvironment
Kosmoceratops is known from the Kaiparowits Formation of Utah, which dates to the late Campanian age of the Late Cretaceous epoch, and occurs in a
Other
In 2010, the paleontologist Michael A. Getty and colleagues examined the taphonomy of the holotype and the subadult specimen UMNH VP 16878 and the sedimentological circumstances under which they were preserved. The more or less articulated holotype specimen was found in a
Paleobiogeography
Though the area of Laramidia was only 20 percent that of modern North America, it saw a major evolutionary radiation of dinosaurs, including the common hadrosaurs and ceratopsians. It has been postulated that there was a latitudinal array of dinosaur "provinces" or biomes on Laramidia during the Campanian and Maastrichtian ages of the Late Cretaceous, the boundary lying around modern northern Utah and Colorado; the same major clades are known from the north and south but are distinct from each other at the genus and species levels. This hypothesis has been challenged; one argument claims that northern and southern dinosaur assemblages during this time were not coeval but reflect a taxonomic distribution over time, which gives the illusion of geographically isolated provinces, and that the distinct assemblages may be an artifact of sampling bias between geological formations. Due to a lack of well-dated fossils from southern Laramidia, this idea had been difficult to test, but discoveries in the Kaiparowits Formation have increased knowledge of fossil vertebrates from the region during the Late Cretaceous. The evolutionary radiation of ceratopsids appears to have been restricted both in time and geographically (the turnover of species was high, and each existed for less than a million years), most taxa being known from latest Cretaceous sediments in the Western Interior Basin, therefore appearing to have originated and diversified on Laramidia.[2][44]
The discovery of Kosmoceratops and Utahceratops greatly increased the number of known chasmosaurines from the Western Interior Basin. Sampson and colleagues viewed this as the strongest support for the idea of dinosaur "provinces" in their 2010 description. They pointed out that in contrast to the Maastrichtian, the preceding Campanian stage had a better sampled, diverse, and far-ranging dinosaur assemblage, as well as more precise geographical and stratigraphical data. The stratigraphic ranges of Kosmoceratops and Utahceratops show that they lived at the same time and likely in the same ecosystems, which was rare among ceratopsids. According to Sampson and colleagues,
Sampson and colleagues stated that their study was the first time intracontinental
Though late Campanian dinosaurs on Laramidia were larger than most large modern animals (which require large species ranges due to heightened dietary needs), Sampson and colleagues found that they appeared to have had relatively small species ranges, which is more perplexing due to the high species-diversity of Laramidian dinosaurs. Though they apparently inhabited at least two semi-isolated regions, there is no evidence of a dispersal barrier, and there was less of a temperature gradient than today. The dinosaurs there appear to have been sensitive to latitudinal zonation in environment (potentially due to lowered physiologies or the environments being more productive), which possibly persisted for at least 1.5 million years. Alternatives to the existence of a barrier include that the discrete provinces were separated by zones of faunal mixing, or that there was a continuous gradient or cline throughout the altitude, with no distinct endemic zones. Possible physical barriers to dispersal include an unidentified mountain range from east to west, flooding in the plain regions by the Western Interior Seaway (which would have temporarily eliminated low-elevation habitats in central Laramidia), or a major river system. Sampson and colleagues considered it more likely that there had been a
In 2012, the paleontologist Terry A. Gates and colleagues suggested that the increase in North American dinosaur biodiversity during the Campanian was due to
With his 2014 assignment of skull CMN 8801 to Kosmoceratops sp. and his naming of a new species of Pentaceratops (P. aquilonius), both from the Dinosaur Park of Alberta, Longrich argued against the idea of distinct northern and southern dinosaur provinces, since the two genera were now known from both southeastern and northern North America. Since northern animals did differ from their southern counterparts, he agreed that there was significant endemism during the Campanian, but found that dinosaur lineages were able to disperse for long distances and were not constrained by geographic barriers, climate, or flora, endemism instead being the result of established (and locally adapted) populations excluding migrant dinosaurs through competition.[7] In 2016, Campbell and colleagues assigned CMN 8801 back to Chasmosaurus, and supported the idea that Kosmoceratops was restricted to southern Laramidia.[17] The same year, Mallon and colleagues found P. aquilonius to be an invalid nomen dubium (dubious name) and agreed that there had been a dispersal barrier between north and south Laramidia. They suggested that the close relationship between Kosmoceratops and Spiclypeus from Montana in the north indicated there had been some short-lived geographic connection.[29]
In 2016, the paleontologist Spencer G. Lucas and colleagues criticized the idea of north–south dinosaur provinciality in Laramidia, and found the case for endemism among non-dinosaurian vertebrates weak, and that of dinosaurs problematic, as mainly a few chasmosaurine taxa were used to identify it. They rejected the idea of dinosaur endemism and provinciality because of problems with sampling biases (the impression that dinosaurs diversified during the Campanian is a result of the denser fossil record from this time), a lack of
In 2017, Fowler pointed out that the date of the Kaiparowits Formation which had been used by Sampson and colleagues to demonstrate that Kosmoceratops and Utahceratops were coeval with chasmosaurines from other formations in the north, had been calibrated differently from those of the other formations. When recalibrated to the same standards, he showed that the stratigraphic overlap between these taxa was not recognized. Instead, only the lower part of the Kaiparowits Formation overlapped with the Dinosaur Park Formation, but this part does not contain Kosmoceratops and Utahceratops, whereas fragmentary remains suggest that some taxa were shared between the formations at this range. Fowler therefore found it more likely that the differences in dinosaur taxa between the formations were due to sampling different stratigraphic levels rather than biogeographic segregation, an explanation he also found probable for the differences between the Kaiparowits Formation and the Fruitland and
While not supporting endemism, Fowler and Fowler suggested in 2020 that there would have been a subtle gradational provincialism of chasmoraurines from North to South, with the lineage including Chasmosaurus being more abundant in the North, Kosmoceratops being its southernmost member, while the lineage including Pentaceratops was more abundant in the South. Since the two clades overlapped geographically during the uppermost part of the middle Campanian, the speciation event that led to the two lineages may have been caused by latitudinal vicariance prior to the appearance of the first member of the Chasmosaurus lineage, 77 million years ago. By 76 million years ago, the supposed barrier dividing the lineages must have disappeared, as they coexisted afterwards; the dividing line appears to have been located somewhere between southern Utah and northern Montana.[20] Fowler and Fowler also found that Vagaceratops lived about 76.2 million years ago while Kosmoceratops lived about 76–75.9 million years ago, and did not overlap stratigraphically.[18]
See also
References
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