The first ceratopsian remain known to science was discovered during the U.S. Geological and Geographical Survey of the Territories led by the American geologist F.V. Hayden . Teeth discovered during an 1855 expedition to Montana was first assigned to hadrosaurids and included within the genus Trachodon . It was not until the early 20th century that some of these was recognized as ceratopsian teeth . During another of Hayden 's expeditions in 1872 , Fielding Bradford Meek found several giant bones protruding from a hillside in southwestern Wyoming . He alerted paleontologist Edward Drinker Cope , who led a dig to recover the partial skeleton . Cope recognized the remains as a dinosaur , but noted that even though the fossil lacked a skull , it was different from any type of dinosaur then known . He named the new species Agathaumas sylvestris , meaning " marvellous forest @-@ dweller " . Soon after , Cope named two more dinosaurs that would eventually come to be recognized as ceratopsids : Polyonax and Monoclonius . Monoclonius was notable for the number of disassociated remain found , including the first evidence of ceratopsid horns and frills . Several Monoclonius fossils was found by Cope , assisted by Charles Hazelius Sternberg , in the summer of 1876 near the Judith River in Chouteau County , Montana . Since the ceratopsians had not been recognised yet as a distinctive group , Cope was uncertain about much of the fossil material , not recognizing the nasal horn core , nor the brow horns , as part of a fossil horn . The frill bone was interpreted as a part of the breastbone .