D. horridus is known only from a set of teeth found in the Late Cretaceous Judith River Formation of Montana and named by paleontologist Joseph Leidy in 1856.

In a 1922 study, William Diller Matthew & Barnum Brown found that the teeth of D. horridus and G. libratus were indistinguishable from each other, and that they almost certainly belonged to the same species.

[3][4] In a 1970 review, Dale Russell stated that because the teeth of D. horridus could not be distinguished from either G. libratus or his newly described species Daspletosaurus torosus, it must be considered a nomen vanum ("empty name").

[6] Additionally, several researchers have agreed that the genus Aublysodon (including the species A. mirandus and A. lateralis), should also be considered a synonym of Deinodon, since it is based on incisor teeth that likely come from the same animal.

[2][3][6] Lambe (1902) went further, and said that as originally named, Deinodon was not preoccupied, and instead, regarded Aublysodon as a nomen nudum.