| Nedoceratops | |
|---|---|
 | |
| Skull from multiple angles | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ceratopsia |
| Family: | †Ceratopsidae |
| Subfamily: | †Chasmosaurinae |
| Tribe: | †Triceratopsini |
| Genus: | †Nedoceratops Ukrainsky,2007 |
| Species: | †N. hatcheri |
| Binomial name | |
| †Nedoceratops hatcheri (Lull vide Hatcher, 1905) OriginallyDiceratops, preoccupied by Förster,1868 | |
| Synonyms | |
| |
Nedoceratops (meaning "insufficient horned face") is a controversialgenus ofceratopsiddinosaur from theLate CretaceousperiodLance Formation ofNorth America. It is known only from a singleskull discovered inWyoming. Its status is the subject of ongoing debate amongpaleontologists: some authors considerNedoceratops a valid, distinct taxon, while others consider it to be an unusual specimen ofTriceratops.[1]
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The nearly complete skullUSNM 2412, the holotype specimen ofNedoceratops hatcheri, was found in eastern Wyoming in 1891, inNiobrara County nearLightning Creek.
The paper that describedNedoceratops was originally part ofO. C. Marsh'smagnum opus, hisCeratopsidaemonograph. Marsh died in 1899 before the work was completed, andJohn Bell Hatcher endeavored to complete theTriceratops section. However, he died oftyphus in 1904 at the age of 42, leaving the paper still incomplete. It fell toRichard Swann Lull to complete the monograph in 1905, publishing Hatcher's description of a skull separately and giving it the nameDiceratops hatcheri;[2][3][4]Diceratops means "two horned face."
Since theDiceratops paper had been written by Hatcher, and Lull had only contributed the name and published the paper after Hatcher's death, Lull was not quite as convinced of the distinctiveness ofDiceratops, thinking it primarilypathological. By 1933, Lull had second thoughts aboutDiceratops being a distinct genus and he put it in a subgenus ofTriceratops:Triceratops (Diceratops)hatcheri, includingT. obtusus; largely attributing its differences to being that of an aged individual.[2]
Because theDiceratops name was already in use for ahymenopteran (Förster, 1868), Andrey Sergeevich Ukrainsky gave the animal its current nameNedoceratops in 2007.[5] Unaware that Ukrainsky had already renamed the animal,Octávio Mateus coined another new name for it in 2008,Diceratus.[6][7]Diceratus is thus ajunior synonym ofNedoceratops.[2]
Nedoceratops means "insufficient horned face". The "nedo" is theRussian prefix meaning "insufficient". The suffix "ceratops", common amongceratopsians, means "horned face". It was named in reference to its lack of a nasal horn.
The nearly complete skull known as USNM 2412 is the only fossil attributed toNedoceratops hatcheri.[8] Superficially, it resembles that ofTriceratops, but on closer examination, it differs: specifically, the brow horns stand almost vertically compared to typicalTriceratops skulls, and there also are several holes in the frill (a unique feature ofTriceratops proper is that it has a solid, unperforated frill). However, at least some of these holes show evidence that they are the result of injury or disease.[9] The nasal horn of this specimen is low and rounded, compared with the larger, pointed nose horns of typicalTriceratops specimens,[2] though this feature appears to be within the known range of individual variation forTriceratops.[10]
Thetype species isNedoceratops hatcheri.Nedoceratops belonged to the Ceratopsia (the name is LatinisedGreek for "horned faces"), a group of herbivorous dinosaurs withparrot-like beaks which thrived inNorth America andAsia during theCretaceous Period, which ended roughly 66 million years ago. All ceratopsians became extinct at the end of this era.[2]
Several authors have suggested thatNedoceratops may be directly ancestral toTriceratops, or perhaps its nearest relative. An ongoing debate concerns the status ofTriceratops,Torosaurus, andNedoceratops. In a series of publications, John B. Scannella andJohn R. Horner (2010[8] and 2011[11]) and claimed that the USNM 2412 skull (i.e., ofNedoceratops) belonged to a "young adult"Triceratops.[8] Evidence for this hypothesis included the shapes of theepoccipital andsquamosal bones, and aneck frill (parietal bone) that had "incipient" openings (contrasting with no openings in subadultTriceratops and large openings in adultTriceratops formerly assigned toTorosaurus).[8] These authors suggested that all three "genera" actually represent different aged individuals ofTriceratops.[11] In 2012, Farke proposed a counterargument, and suggested that the bone surface texture and shape of the horns ofNedoceratops indicate an "old adult".[2] A follow-up study by Leonardo Maiorino and colleagues in 2013[10] usingmorphometrics found support forTriceratops andTorosaurus being distinct, valid taxa, withNedoceratops occupying variable positions with respect to the other two but generally outside the range of variation, concluding that "the size of USNM 2412 is a plausible intermediate, but the shape is not."[10]
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Another supposed difference betweenNedoceratops and fossils referred toTriceratops horridus is the remarkably short, rounded nasal "horn". Scanella and Horner proposed that the nasal horn of the USNM 2412 skull could have been lost when the animal was alive or when it became fossilized.[8] However, it has been noted the horns of ceratopsids show a great deal of variation between age groups and individuals, and some specimens more solidly attributed toT. horridus have a similar nasal horn shape. In most features- the short, saddle-shape frill, the s-shaped snout- the animal closely resemblesTriceratops horridus.[12]
It has been noted that many of the features that seem to separateNedoceratops fromTriceratops, and specificallyTriceratops horridus, may be the result of pathology, injury, and/or deformation of the skull after burial. Two of the features that have been used to diagnoseNedoceratops - the position of the squamosal and the upright brow horns- are seen on one side of the skull, but not the other. This, along with the fact that the entire skull can be seen to be twisted when seen head-on, have been used to argue that these features result from post-mortem distortion of the fossil, rather than reflecting the anatomy of the animal during life. Furthermore, the presence of numerous holes in the frill suggests pathology due to injury or illness, the supposedly unique 'parietal fenestrae' may therefore be the result of an injury. Tanke & Farke (2007) noted that the supposed parietal fenestra had an irregular shape with swollen margins and an irregularly vascularized texture. This is similar to a parietal hole, also interpreted as the result of an injury by Marshall & Barreto (2001), in a specimen ofTorosaurus.[9] The frill is only preserved on one side, which makes it difficult to test this hypothesis.
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