[2] Stegomastodon is suggested to have ultimately originated from New World populations of Gomphotherium, possibly via the intermediate genus Rhynchotherium.

[3] The earliest species of the genus appeared during the Pliocene (Blancan) around 3-4 million years ago.

During the early Irvingtonian, around 1.2 million years ago, Stegomastodon became extinct, which is suggested to be due to competition with the recently arrived mammoths, which were more efficient grazers.

[3] Originally, some specimens from Jalisco, Mexico were estimated to date to 28,000 years Before Present,[4] but this age was rejected in 2011 by Spencer G. Lucas et.

[5] The South American Stegomastodon fossils have been reassigned to Notiomastodon by the majority of recent authors.