9. First Discovery of American Dinosaurs, 1856
This is a very short, two-page paper, with no illustrations to arrest the eye, but if one takes the time to read the text, or even just the headings, a remarkable document comes alive. Ferdinand V. Hayden, in 1855, had conducted a geological survey along the Judith River in the Nebraska Territory, and he had found a number of large fossilized teeth belonging to some unknown animals. Hayden sent the specimens to Joseph Leidy, a physician and eminent naturalist of Philadelphia. Leidy recognized that some of these were the teeth of very large reptiles, and in this paper he identified and named eight genera, of which three turned out to be dinosaurs: Trachodon, Troodon, and Deinodon. This paper is the first published description of dinosaur remains in the United States. Leidy truly understood what he had found; although his Trachodon was classified primarily on the basis of one tooth, Leidy observed that it was an animal similar to Iguanodon, and he commented that the Deinodon teeth, although fragmentary, resembled those of Megalosaurus.
In an article published in 1860, Leidy included a plate with an illustration of the Trachodon tooth.
Leidy, Joseph. "Notice of remains of extinct reptiles and fishes, discovered by D. F. V. Hayden in the Bad Lands of the Judith River, Nebraska Territory," in: Proceedings of the Academy of Natural Sciences of Philadelphia, vol. 8 (1856), pp. 72-73. This work was on display in the original exhibition as item 9.