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Eotriceratops (meaning "dawn three-horned face") is a genus of herbivorous ceratopsian which lived in the area of North America during the late Cretaceous period. The only named species is Eotriceratops xerinsularis.
The holotype specimen, RTMP 2002.57.5, was found in a layer of the uppermost Horseshoe Canyon Formation, dated to the early Maastrichtian, about 68.8 million years ago. It consists of a partial skeleton with much of the skull; the skull lacks the lower jaws but includes parts of the edges of the frill, large horns above the eyes, and a small horn above the nose, similar to the closely related Triceratops. At least seven neck and five back vertebrae, as well as several ribs and ossified tendons, were also recovered. The bones were largely found disarticulated. Because the specimen was found in weakly bedded shale, many of the bones were badly crushed.
In 2010, Gregory S. Paul renamed the species Triceratops xerinsularis, but this inclusion of Eotriceratops in the existing genus Triceratops has not been followed by other researchers.
Possible additional specimens, which have been variously included in the species Ojoceratops fowleri and Torosaurus utahensis, are known from the same time period in New Mexico and may also belong to Eotriceratops.
Eotriceratops differs from other chasmosaurine ceratopsians in unique features of the skull bones. In 2007, several autapomorphies, unique derived traits, were established. The process of the praemaxilla, obliquely protruding to above and behind in the bony nostril, does not have a groove or depression on its outer side contrary to the situation with Triceratops; this process is exceptionally wide in side view; it also reaches above the level of the lower border of the fenestra interpraemaxillaris. The episquamosals, the epoccipitals of the squamosal, thus the skin ossifications lining and often protruding from the edge of the frill, have an extremely elongated base, and are flattened and spindly, touching each other as with Torosaurus. Near the lower edge of the squamosal a clearly demarcated groove or depression is present. On the lower front of the nasal horn core, a vertical, slightly obliquely running, vein groove meets second vein groove, running horizontally. The epijugal forms an unusually pronounced sharp jugal horn. At its rear upper side the epijugal bears a pronounced process, pointing to behind. A depression on the top of the epijugal forms a contact facet with the jugal; a depression at its inner side forms a separate facet contacting the quadratojugal.
The snout of Eotriceratops was relatively flat and elongated. The depressions on the sides of the praemaxillae were connected through an oval fenestra interpraemaxillaris; small rounded processes pointed to above and behind into this opening, originating from the front lower edges. The strut between this opening and the nostril was narrow in side view and transversely thickened with a straight rear edge. The processes jutting into the nostrils had hollow outer sides but were far less excavated and much higher than with Triceratops or Torosaurus. The maxilla bore at least thirty-five tooth positions. The nasal horn was low, situated above the nostril and slightly recurved. It had a narrow rear edge and a transversely flattened point. The horns above the eyes were forward-curving and have been estimated at long. The lower base of these horns was narrow and vertically directed, which with Triceratops is a juvenile trait. Three bite marks can be observed above the eye, near the base of the left horn, which were interpreted as traces of scavenging. The squamosal shows at least five episquamosals. Little has been preserved of the forming the centre of the neck shield.
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