|JuraPark in Solec Kujawski, Poland. Image credit: CLI / CC BY-SA 3.0|
The first named Triceratops was initially discovered in 1887 in Denver, Colorado and consisted of brow horns and a portion of the skull roof to which they were attached. An earlier specimen discovered in 1872 in Wyoming was sent to E. D. Cope. Unfortunately, Cope possessed only post-cranial remains which looked very much like those of a hadrosaur. The remains are currently only provisionally considered those of a Triceratops and are still referred to by the name Cope assigned to it: Agathaumas sylvestris Cope, 1872.
The Denver specimen was sent to O. C. Marsh who originally officially named the specimen Bison alticornis. Marsh reconsidered and renamed the animal after an 1888 discovery by John Bell Hatcher in Wyoming. This was the third specimen presented to Marsh and apparently finally consisted of enough skull material to convince the professor that rather than a Pliocene mammal he was looking at one of those "Ceratops dinosaurs" he had published on sometime between 1887 and 1889 when the newly minted and now official name Triceratops horridus was published. This is the name we use now, in addition to a second recognized species, T. prosus Marsh 1890.