For 10 points, identify this herbivorous dinosaur, named for the three horns on its face.
In 1961, Bruce Erickson discovered a remarkably complete specimen of this organism at the Hell Creek Formation. A 1907 monograph written by Richard Swann Lull describes a tertiary lineage of this organism including the species obtusus and hatcheri, though the only species recognized now are prorsus and the type species, horridus. This animal's front legs had five fingers, while the rear had only four. According to John Scannella and Jack Horner, the observed size differences in the length of their epoccipital-bone-lined frills was a result of adult specimens of this creature being mistakenly classified as Torosaurus. It lived the Cretaceous period alongside its primary predator, Tyrannosaurus Rex. For 10 points, identify this herbivorous dinosaur, named for the three horns on its face.
In 1961, Bruce Erickson discovered a remarkably complete specimen of this organism at the Hell Creek Formation.
{Triceratops} [prompt on {Torosaurus} before mentioned; accept it {along} with any of the {given species} names]