Achelousaurus

Taxobox|
name = "Achelousaurus"

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image width = 200px
fossil_range = Late Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Marginocephalia
superfamilia = Ceratopsia
familia = Ceratopsidae
subfamilia = Centrosaurinae
genus = "Achelousaurus"
genus_authority = Sampson, 1995
subdivision_ranks = Species
subdivision =
*"A. horneri" Sampson, 1995 (type)

"Achelousaurus" (typically pronEng|əˌkiːloʊˈsɔrəs, though IPA|/ˌækɨˌloʊəˈsɔrəs/ might be a better reflection of the butchered etymology; ["Since the scientific name "Achelousaurus" was formed by arbitrarily combining "Achelous" (IPA|/ˌækɨˈloʊəs/) and "saurus" instead of using the stem-form "Achelo-," the "u" needs to be pronounced." [http://dml.cmnh.org/1999May/msg00731.html] ] "Achelous's lizard") is a genus of centrosaurine ceratopsid dinosaur from the Late Cretaceous Period of what is now North America. It was a quadrupedal herbivore with a parrot-like beak, a rough boss (raised bony area) on the snout and two more behind the eyes, and two horns on the end of its long bony neck frill. With a total body length of 6 meters (20 feet), "Achelousaurus" was a medium-sized ceratopsian.

The genus and the one named species ("A. horneri") were both named by paleontologist Scott Sampson in 1995. The specific name honors Jack Horner, an influential American paleontologist famous for his Montana dinosaur discoveries. The generic name "Achelousaurus" is a complex reference to Greek mythology. Achelous, an important Greek river deity, had one of his horns torn off by Hercules, in a mythological fight with the legendary hero. All three known skulls of "Achelousaurus" have rough bosses in the same places where other ceratopsians had horns, giving it the appearance of having had its horns ripped off. Achelous was also celebrated for his shapeshifting ability, just as "Achelousaurus" appears to combine features of other ceratopsian dinosaurs. Early reports suggested that "Achelousaurus" represented a transitional form between ceratopsians with modified horns like "Einiosaurus" (with which "A. horneri" shares two horns on the end of the frill), and the derived, hornless "Pachyrhinosaurus" (Horner et al., 1992). While they may or may not form a direct line of descent, all three of these species are at least closely related, and are often united in the tribe Pachyrhinosaurini, inside the subfamily Centrosaurinae and the family Ceratopsidae (Sampson, 1995; Dodson et al., 2004).

"Achelousaurus" is known from the U.S. state of Montana, in the Two Medicine Formation, which preserves sediments dated from the Campanian stage of the Late Cretaceous Period, between 83 and 74 million years ago. "Achelousaurus" was found in the highest levels of the formation, so it is probably closer to the end of that timeframe. Other dinosaurs found in this formation include "Daspletosaurus", "Bambiraptor", "Euoplocephalus", "Maiasaura", and "Einiosaurus".

Scientists have so far recovered three skulls and some postcranial material from the Two Medicine, all housed at the Museum of the Rockies in Bozeman, Montana. The skull of a full-grown "Achelousaurus" (including the frill horns) is over 5 feet (1.6 meters) long.

References

*Dodson, P., Forster, C.A., & Sampson, S.D. 2004. Ceratopsidae. In Weishampel, D.B., Dodson, P. & Osmolska, H. (Eds.) "The Dinosauria" (2nd Edition). Berkeley: University of California Press. Pp. 494-513.
*Horner, J.R., Varricchio, D.J. & Goodwin, M.B. 1992. Marine transgressions and the evolution of Cretaceous dinosaurs. "Nature" 358: 59-61.
*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.

External links

* [http://www.dinodata.org/index.php?option=com_content&task=view&id=6076&Itemid=67 "Achelousaurus" at Dinodata]