English: Achelousaurus horneri Sampson, 1995 - fossil ceratopsian dinosaur skull from the Cretaceous of Montana, USA. (Holotype - MOR 485, Museum of the Rockies, Bozeman, Montana, USA)

Ceratopsians are the "horned dinosaurs". They were large, quadrupedal, herbivorous dinosaurs having a beaked skull and a frill - an extension of bone behind the skull that partially covered the neck. Ceratopsian dinosaurs are known from the Jurassic and Cretaceous. The last members of the group died out at the Cretaceous-Tertiary boundary, 65 million years ago.

Seen here is a partial adult skull of Achelousaurus horneri, currently only known from the Cretaceous of Montana. Rough protuberances ("bosses") are present on the snout and above the eyes. The faces of inferred younger skulls of this species were horn-bearing. The openings in the frill are called fenestra - their presence reduced the weight of the skull.

Classification: Animalia, Chordata, Vertebrata, Reptilia, Archosauria, Dinosauria, Ornithischia, Marginocephalia, Ceratopsia, Ceratopsidae

Stratigraphy: Two Medicine Formation, Campanian Stage, upper Upper Cretaceous

Locality: undisclosed site in the Landslide Butte area, northeastern Glacier County, northwestern Montana, USA

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Info. at:

en.wiki.x.io/wiki/Achelousaurus