For many years, "Triceratops" finds were known only from solitary individuals. These remains are very common: one palaeontologist reported having seen 200 specimens of "T. prorsus" in the Hell Creek Formation of Montana, U.S. Similarly, Barnum Brown claimed to have seen over 500 skulls in the field. "Triceratops" teeth, horn fragments, frill fragments, and other skull fragments are abundant fossils in the latest Upper Cretaceous of western North America. It was the most dominant herbivore of the time. In 1986, Robert Bakker estimated it as making up 5/6ths of the large dinosaur fauna at the end of the Cretaceous.