Open Paleo

Achelousaurus

Sampson, 1995 ak-e-LOH-uh-SAWR-us /əˌkiːloʊˈsɔːrəs, ˌækɪˌloʊəˈsɔːrəs/

Named after Achelous, the Greek deity of rivers, combined with Greek 'sauros' meaning 'lizard'; meaning 'Achelous lizard'

83.6–72.2 million years ago Campanian, Late Cretaceous
Late Cretaceous stages

Achelousaurus is a genus of centrosaurine ceratopsid dinosaur that lived during the Late Cretaceous Period of what is now North America, about 77 to 74.8 million years ago. The first fossils of Achelousaurus were collected in Montana in 1987, by a team led by Jack Horner, with more finds made in 1989. In 1994, Achelousaurus horneri was described and named by Scott D. Sampson; the generic name means "Achelous lizard", in reference to the Greek deity Achelous, and the specific name refers to Horner. The genus is known from a few specimens consisting mainly of skull material from individuals, ranging from juveniles to adults.

Diagnosis

  1. Relatively small, thin, heavily-pitted nasal boss in adults restricted to the nasal region.
  2. Relatively large, high-ridged supraorbital bosses in adults rather than true horns.
  3. Sub-adults possessing true supraorbital horncores with concave surfaces medially.
  4. Parietal with single pair of curved spikes projecting posterolaterally from the rear margin.

Species

Achelousaurus horneri Sampson, 1995

Type species

Named for Jack Horner, who led the team that first collected fossils of this dinosaur in Montana in 1987.

Holotype
MOR 485 , Museum of the Rockies
Material
Partial skull including nasal boss, supraorbital bosses, and parietal.
Horizon
Two Medicine Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
Landslide Butte Field Area, Montana, United States

References

  1. Sampson, S. D. (1995). Two new horned dinosaurs from the Upper Cretaceous Two Medicine Formation of Montana; with a phylogenetic analysis of the Centrosaurinae (Ornithischia: Ceratopsidae). Journal of Vertebrate Paleontology 15(4): 743-760. doi:10.1080/02724634.1995.10011259 sampson1995a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the hip height estimate, and the appearance features.

    jones2026a