Nedoceratops

Single sampleUSNM 2412 is an almost complete skull with no lower jaw , up to 1.8 meters long ^[2] .

Autotapomorphies include a reduced nasal horn, almost indistinguishable from the nasal bone , eyebrows horns facing upwards (at right angles to the jaw line), and very small windows in the parietal bone ^[2] .

There are obvious pathologies on the skull - for example, the asymmetry of the windows and the bones around them (strong thickening on the left side of the skull compared to the right) ^[2] . According to (1933), the area of ​​the left scaly bone was severely affected by a certain disease, and since one of the muscles important for head movements was attached, the animal could not move its head normally ^[3] .

The holotype was discovered in 1891 by John Hetcher and his field team in Nyobrera County, Wyoming , USA , in a sandstone nodule ^{[4] [3]} . Hatcher was going to describe it as a new species and genus, but died in 1904, without completing the work. In 1905, Richard Swann Lall named the find Diceratops hatcheri ^[4] . Later, however, Lall began to doubt her belonging to a separate genus (retaining confidence in the independence of the species), in particular because he considered holes in the skull arising from injuries or illness. In 1933, he classified it as Triceratops hatcheri ^{[3] [2]} .

In 1986, John Ostrom and Peter Wellnhofer , making a revision of the Triceratops genus, concluded that all known finds can be attributed to one species - Triceratops horridus , although the independence of several other species, including T. hatcheri , is not excluded ^[5] . In the publications of 1990 ^[6] and 1996 ^[7] , proposed to restore Diceratops as a valid genus. Many experts did not support this conclusion, continuing to consider D. hatcheri a synonym for T. horridus ^[2] . In 2007, Wu Xiaochun et al. Published the results of a cladistic analysis based on morphological characters, according to which Diceratops is a separate genus of the hazmozavrin subfamily and a closer relative of the torosaur than Triceratops ^[8] .

In 2007, the Russian entomologist Andrei Ukrainsky discovered that the name Diceratops was used in 1869 by Arnold Förster for the insect genus, and proposed a new name for the dinosaur genus Nedoceratops , meaning “full-horned muzzle” (due to the absence of a nasal horn) ^[9] . The following year, the Portuguese paleontologist who did not know about this proposed to rename Diceratops to Diceratus ^[10] , but the name Nedoceratops , as previously published, takes precedence ^{[11] [2]} .

In 2010, John Horner and John Scanella came to the conclusion that Nedoceratops is a transitional form between young and adults of Triceratops (and the torosaur is his adult) ^{[12] [13]} . The following year, this was challenged by Andrew Farke: on the basis of a number of signs, he found that the skull of Nedoceratops belonged to a completely adult individual and concluded that triceratops, torozavr and, probably, Nedoceratops are independent genera ^[2] . In 2013, the same result was obtained in a study by Leonardo Majoro, Andrew Farke, et al. ^[14] Nicholas Longrich and co-authors in a number of publications (2011 ^[15] , 2012 ^[16] , 2014 ^[17] ), agreeing that these forms are not age stages, considering that Nedoceratops differs from Triceratops as insufficient for its isolation into a separate genus. This opinion as of 2018 is shared by the majority of specialists ^[1] .

• Black R. Nedoceratops: To Be, Or Not To Be? (eng.) Smithsonian (December 15, 2011). Archived October 18, 2016.
• Berkowitz B., Blanchard S., Florit G., Shin Y. The mystery dinosaur . Stuff (September 20, 2018). Archived December 6, 2018.
• Nedoceratops hatcheri (Lull, 1905) (Neopr.) . National Museum of Natural History. Archived July 9, 2019.