At one time, Cope and Marsh were friends. The two had met in Berlin, Germany in 1864, and spent several days together. They even named species after each other. Over time, however, their relations soured, due in part to their temperaments. Cope was known to be pugnacious and possessed a quick temper; Marsh was slower, more methodical, and introverted. Both were quarrelsome and distrustful. The two men's scientific theories were on occasion drastically different; Cope was a firm supporter of Neo-Lamarckism, while Marsh supported Charles Darwin's theory of evolution by natural selection. Even while friends, both men were inclined to look down on each other subtly. As one observer put it, "The patrician Edward may have considered Marsh not quite a gentleman. The academic Othniel probably regarded Cope as not quite a professional."
Cope and Marsh came from very different backgrounds. Cope was born into a wealthy and influential Quaker family based in Philadelphia. Although his father wanted his son to work as a farmer, Cope instead distinguished himself as a naturalist. In 1864, Cope became a professor of zoology at Haverford College and joined Ferdinand Hayden on his expeditions west. Marsh would have grown up poor, the son of a struggling family in Lockport, New York, had it not been for the benefaction of his uncle, philanthropist George Peabody. Marsh persuaded his uncle to build the Peabody Museum of Natural History, placing Marsh as head of the museum. Combined with the inheritance he received from Peabody upon his death in 1869, Marsh was financially comfortable (although due in part to Peabody's stern views on marriage, Marsh would remain a lifelong bachelor).
On one occasion, the two scientists had gone on a fossil-collecting expedition to Cope's marl pits in New Jersey, where William Parker Foulke had discovered the holotype specimen of Hadrosaurus foulkii, described by the paleontologist Joseph Leidy;...