Nedoceratops

Nedoceratops (meaning "insufficient horned face") is a controversial genus of ceratopsid dinosaur from the Late Cretaceous period Lance Formation of North America. It is known only from a single skull discovered in Wyoming. Its status is the subject of ongoing debate among paleontologists: some authors consider Nedoceratops a valid, distinct taxon, while others consider it to be an unusual specimen of Triceratops.

The nearly complete skull USNM 2412, the holotype specimen of Nedoceratops hatcheri, was found in eastern Wyoming in 1891, in Niobrara County near Lightning Creek.

The paper that described Nedoceratops was originally part of O. C. Marsh's magnum opus, his Ceratopsidae monograph. Marsh died in 1899 before the work was completed, and John Bell Hatcher endeavored to complete the Triceratops section. However, he died of typhus in 1904 at the age of 42, leaving the paper still incomplete. It fell to Richard Swann Lull to complete the monograph in 1905, publishing Hatcher's description of a skull separately and giving it the name Diceratops hatcheri; Diceratops means "two horned face."

Since the Diceratops 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 of Diceratops, thinking it primarily pathological. By 1933, Lull had second thoughts about Diceratops being a distinct genus and he put it in a subgenus of Triceratops: Triceratops (Diceratops) hatcheri, including T. obtusus; largely attributing its differences to being that of an aged individual.

Because the Diceratops name was already in use for a hymenopteran (Förster, 1868), Andrey Sergeevich Ukrainsky gave the animal its current name Nedoceratops in 2007. Unaware that Ukrainsky had already renamed the animal, Octávio Mateus coined another new name for it in 2008, Diceratus. Diceratus is thus a junior synonym of Nedoceratops.

Nedoceratops means "insufficient horned face". The "nedo" is the Russian prefix meaning "insufficient". The suffix "ceratops", common among ceratopsians, 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 to Nedoceratops hatcheri. Superficially, it resembles that of Triceratops, but on closer examination, it differs: specifically, the brow horns stand almost vertically compared to typical Triceratops skulls, and there also are several holes in the frill (a unique feature of Triceratops 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. The nasal horn of this specimen is low and rounded, compared with the larger, pointed nose horns of typical Triceratops specimens, though this feature appears to be within the known range of individual variation for Triceratops.

The type species is Nedoceratops hatcheri. Nedoceratops belonged to the Ceratopsia (the name is Latinised Greek for "horned faces"), a group of herbivorous dinosaurs with parrot-like beaks which thrived in North America and Asia during the Cretaceous Period, which ended roughly 66 million years ago. All ceratopsians became extinct at the end of this era.